On the casino literature, it says the Free Play are available Sunday
through Sat.
Here's a warning, if you come Sat night at 10 pm and use your free
play, then it doesn't become available at 12:01 Sunday morning*. The
system is designed (as I was told) that next week's free play won't be
released until the following Monday 8 am.
Cheers.
* In some casinos, the free play becomes available at 12:01 so there
is usually a long of people line waiting for next day's free play.