There is no stated elite benefit for early check-in, only late check-outs. But I've had very good luck with being able to check-in early at Marriotts, especially at the Marriotts at international gateway cities where it may be common for people to arrive early from flights.

Probably your best option is what JCPTX suggests and call the hotel directly to see what their normal policy is. If they aren't too full when you arrive and have a room available, they may let you go ahead and check-in. If they are closer to full and don't have a room, (and assuming you are a Gold/Plat, they may let you wait in the CL while they get you a room.

Also note that a lot of this depends on what you mean by "early". If your talking about pre-breakfast early and you really want a room, you might need to actually reserve the room for the previous night. If by early you mean 10am-noon timeframe, then the hotel may try to work with you if they can.