Gold is the other elite level with SPG. There is only a 4 pm guaranteed late checkout for platinum members at SPG.

As a silver member with Marriott, you are behind all the gold, platinum and platinum premier members on the status totem pole. Usually, you should be able to get 1-2 extra hours at FS properties as a silver member, although they might not be as generous if they are busy. A late checkout is usually harder at limited service properties since they have less housekeeping.

At Marriott properties, I have little trouble getting two extra hours past the regular checkout time. I have occasionally asked for 2.5 hours extra, but it is pretty hard to get more than 2 hours unless you are a regular at a hotel, their occupancy is really low, or you have some extenuating circumstance.

You should have better odds getting a late checkout at one of the airport hotels since there are more guests who leave early to catch early flights. The Renaissance LAX has a 1 pm normal checkout vs noon for the Marriott LAX.