There are some companies and practices that are active even on weekends that'll take odd days off. Perhaps the guys who were available to take make the tow work Saturdays or even Sundays, and so they take Mondays off as compensation. There are some offices that work Saturdays and do a lot of business on Saturdays (because people work during the week) that are closed on Mondays: our dentist, various hair salons, etc. Alternatively, they already had their appointments booked up for Monday, or else they were booked on Saturday (probably a busy day for them), and so these guys regularly took Mondays off, but worked Saturdays and were already booked. Could be anything, but there's no holiday on Monday ... unless you've got some special Tejas thing going on down there, like a March-teenth.

(transferred to Monday due to the 18th/19th being weekend days).