What does "end of time" (as is often used to describe the end of the world) actually mean? Surely there will be chronology in the new heaven and earth. So how can we say "End of time"? Isn't only God outside of time? Doesn't the Book of the Apocalypse speak of "30 minutes in heaven"?

Does it simply mean the end of this particular time?

Will the calendar be reset in the new heaven and earth?

What will happen when, in eternity, the number of years becomes so large that writing the numerical year becomes difficult due to the sheer number of digits?

Will there be Mass in the new heaven and earth since the Holy Mass has been established in "perpetuity"?

Also, those prayers of the Mass that would be "obsolete" in the new heaven and earth -- e.g. prayers for the dead -- will they be omitted? And on whose authority would the Mass be changed?

Yes, I realise these questions sound silly. But silly questions like these are what constantly bother me and cause a bit of anxiety for me, truth be told. I wonder if anyone else, more knowledgeable and wiser about these matters than I, can offer insights.

:)

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There has been some speculation on this subject by Church theologians and philosophers.
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Bottom line, there is a lot of mystery involved so some words might seem contradictory or inconsistent, but at least some of the confusion comes from the doctrine that in the next world time A) will be no more, or B) will be very different from the time we now know.
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A and B are not mutually exclusive and can be seen as two different ways of looking at the same thing.
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A reason the rules on indulgences were changed is because saying there is no time as we know it in the next world makes it hard to explain what a 7 days' indulgence means, compared to 40 days or a quarantine, if there is no time, as such, in Purgatory. If it's not "time as we know it," then why say "days" or "quarantines" (which refers to a length of time on the calendar, similar to the duration of Lent).
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One of the attributes that angels enjoy is agility, which means the ability to move through the universe at the speed of thought. Well, to our way of thinking, speed implies the passing of time. The saints in heaven will share this angelic faculty of agility so that they will be able to move with the speed of thought, but what does that have to do with there being no time as we know it?
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As St. Paul says, we see now imperfectly, as through a glass darkly, but then we shall see with vision clear.
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A lot of the Protestant and other non-Catholic errors come from their expectation that the next world will be just like this one, so they imagine what their best day has been in their life and project that onto what they would expect every day to be like in heaven. Or take Moslems for example, with their 72 virgins being the be-all-and-end-all of paradise. Did they ever wonder how enjoyable that would be for the virgins? Or Hindus or Buddhists with their so-called meditation consisting of achieving the ultimate goal by emptying the mind of all thought. Nothingness is bliss, then? Not according to Catholic doctrine. 

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What does "end of time" (as is often used to describe the end of the world) actually mean? Surely there will be chronology in the new heaven and earth. So how can we say "End of time"? Isn't only God outside of time? Doesn't the Book of the Apocalypse speak of "30 minutes in heaven"?

I never heard of the "30 minutes" either, I always just believed the end of time is just that, along with the end of time comes the wrath of God - I've always thought of the two as inseparable, as one event that will most certainly happen.

That will be the time when Our Lord comes again, but not in the meekness of the manger or the humility of a Savior, the next time He comes will be as a mighty Judge with all power and majesty to judge the living and the dead, the next ime He comes as the "Judge Severe" as He is called in Dies Irae. His second coming brings with it the end, the termination of time, the termination of human history, and the wrath of Almighty God that the people outside of the Church have brought down upon themselves. "That day of wrath, that dreadful day, shall heaven and earth in ashes lay, as David and the Sybil say..."

Fr. Wathen has an excellent short sermon on this subject, here are a few snips:

"History itself will come to a termination, this termination will be very abrupt and it will cancel all of man's plans, and the everlasting designs of Almighty God will bee seen in their full effect.... The termination of human history will be terrific, it will be frightful, it will be altogether cataclysmic. The Scriptures warn us that finally, God will show Himself.....whether sooner or later, Christ made sure not to indicate, but when it does come, it will be horrendous for those who have not been ready, and that wrath will be everlasting...."     

   

1And when he had opened the seventh seal, there was silence in heaven, as it were for half an hour. (Apoc 8:1)


The "silence" you mention is WAY before Our Lord comes again, it's even before the 7th trumpet has been sounded.  So I don't see a connection at all between the "end of time" and the "silence".

This is the Haydock commentary on this verse:
There was silence in heaven: which is to represent as it were a general consternation, and an expectation of dreadful events at the opening of the seventh seal, and when seven Angels stood prepared to sound seven trumpets.

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"...as it were for half an hour." The words, "as it were" indicate allegory or similitude, in other words not a literal 30 minutes.

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The angels in heaven are not subject to the restrictions of our material world. 
Angels see time, as an attribute of our material world but not of heaven, as an object to be observed from the outside.
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But with God's permission, angels can enter time from their native world beyond time, and then leave time to go outside.
They move in and out of time with the speed of thought, which is due to their attribute of agility.
They enjoy the qualities of subtlety, impassibility, agility and clarity, none of which we have in this material world with our material bodies.
Angels are able also to move through time within the permission granted by God, which generally prohibits them from revealing the future.
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The bad angels (devils) are even more restricted since if they could, they would disobey God in various ways.
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The will of God is always done in heaven: "...thy kingdom come, thy will be done on earth as it is in heaven."

Exactly. I don't understand how people can say there will be no time -- that is, no chronological order of events -- in heaven.  That attribute of being outside of time seems applicable only to God.

That is beautiful, Myrna. Thank you for sharing it.