The slot/VP day runs from 6am-6am. I verified this with days of play
and record keeping, and makes the most sense since the casino is very
crowded at Midnight but dead at 6am. (Lounge day is also based on
6am.) This is a correction from an old post where I said a host told
me it was Midnight-Midnight, which is only true for the daily swipe
machines. At MS, you can swipe at 11:59p and again at 12:01am. (Daily
swipes and slot day at Foxwoods run also 6am-6am. But monthly
promotions start and end on midnight of that month.) For redeeming
gift/gas cards etc it's loosely based on ~3:30am -- whenever they close
out and reset the cash register/computer system; the clerk can often
tell you what day it's on. When I got the gas cards I would go Sunday
at Midnight and then fill up a second time upon leaving. For table
games, it's usually between 4-5:30am when there is a lull or break in
play and it will be noticeable as the floor managers have to count and
fill out paperwork.
What you do not want to do is play all night and then 2 minutes past
6am or a table that's been closed out and reopened, and leave. You
will then be halfing your theo for the day, and make yourself look like
a much smaller player.