This has been my experience and IMHO.....
We have arrived as early as 10am and as late as 11pm.
I really don't think it makes any difference. But I think what Belle1962 says is probably the closest.
When we have arrived early....they give us what is FIRST AVAILABLE. Meaning, if what you have requested will not be ready because the room has to be cleaned, etc...then you won't get it. At that point you have to tell them specifically that you are willing to wait til later in the day in order to get your request, you may wait til really late in the afternoon!
Neeter....you said yourself you had to keep insisting on her looking for something in Toy Story??!!
Also, if arriving early....I doubt you will see any complimentary upgrades...they are waiting to see if anyone checking in asks to be upgraded and are willing to pay!
I think....and this is just IMHO....that the rooms are assigned first thing that morning and they try everything posible to just give out the rooms as they have assigned them with VERY LITTLE adjustments. As the day goes by and there are fewer guests to move around....it is easier to make adjustments.
We have found if we arrive mid-afternoon we have gotten all of our requests.
My DH travels alot and ALWAYS feels a later check in (like after 8pm) is better. There are fewer people in line. And he has had MANY, MANY times when he has been upgraded to a better room because his requests can't be met.....AND.....the better rooms are still available.
The resorts also figure if they give you a taste of a better room this time....when you come back you will be willing to pay for it.
I still think it is the luck of the draw!!
