http://travelupdate.boardingarea.com/marriott-cancel-1159-pm-avoid-penalty-fees-new-policy-says/
Although often you can run into properties with 1, 2, or 3 day prior to reservation cancellation times, the current majority is a cancellation same day of reservation (4 pm or 6 pm). Next year all reservations must be cancelled by (at least) 11:59 pm local time the day before check in.
Thanks to ks77 and kharada46 for sharing, http://travelupdate.com/ a pretty good travel web site with some interesting topics.
And speaking of sharing, as all trends indicate, we're probably better off as Insiders using our energy in sharing deals and warnings vs. bemoaning the inevitable ongoing loss of benefits or tightening of policies.
As James Taylor sang, Marriott's a 
baby, they're bound to roll all over us.
Book those award 5 nights for 4 - while you can 
.