Sometimes an upgrade (or just room assignment) will appear about 24 hrs before check-in. But be advised that what you see is NOT always what you get. I've had several occasions where I checked the room and saw an upgrade, only to arrive and be handed keys to a completely different room. I believe another FTer complained about the same thing just this week in another thread.

It's always a good idea to check and see what rooms are actually available for sale within 24 hrs of check-in (for the amount of nights you are staying). That way you will know what kinds of upgrades might be available. You can then mention to the front desk that you'd 'love one of the jacuzzi rooms' or whatever your preference might be. Always keep in mind that suites are not part of the Marriott guarantee.

Hope that helps.