They seem to be mailed out sporadically. I think I remember socrates posting once that they are mailed out by a contractor and so dates are uncertain.

I usually get them, when I get them, about 45 days before the offers expire. This last one, received in late March with offers good until the end of May, was an exception.

There's no guarantee what each will contain, but I believe all that I've received over the last couple years have had the Marriott and Renaissance "two-for-one" weekend nights offers, and the "buy one dinner entree, get the second free" offers. Those seem to be evergreens.