My profile is currently set up to earn Marriott points for my stays. I want to change this to US Airways shortly (for the Grand Slam) and then change it back to Marriott again. I have two Marriott-specific questions about the speed of this that I hope someone can help me with:

1) Let's say I have already changed my earning to US Airways. I check out of hotel A this morning having earned US miles. Can I call MR during the day to change back to Marriott points and then check into hotel B tonight and earn Marriott points? Is it that fast?

... separate scenario next...

2) Does anyone have any experience during a multi-night stay of having some nights credit to an airline program and then have the remainder credit to MR?

Thanks in advance.

Yes, changing your preferences happens immediately, but my experience is that your earnings will be based on your preferences at the time that your points/miles post, rather than your preferences at the time of the stay.

For example, check in 9/28, check out 9/29. Check into a new hotel 9/29, check out 9/30. On 10/1, points post for stay one. Switch earnings to miles. On 10/2, miles post for stay 2.

Sorry, haven't tried this one.

Thanks! Do you know if MR points post more quickly than airline miles? I seemed to get that impression on one of the Grand Slam threads for hotels in general (i.e. not specific to Marriott). I'm worried that they might only do a 'sweep' for airline miles, say, once a week and all my stays end up getting credited on the same date.

There's a small delay between when your stay posts and when your miles will show up in your frequent flyer account (I've only switched my preferences to miles for the Delta promo last year - with Delta it was just a couple days), but I'm pretty sure once your stay posts with a miles earning preference, that regardless of what you switch your preferences to after that, the miles will be credited to your FF account.