1) As soon after 6:05am as possible, even if the site is not ready.
. . . checking-in prior to 6:05am is considered the night prior by the computer
. . . you can easily get charged and extra day
2) If you don't like your site, it is early enough to have the CM change the site for you.
3) Regarding Resort rooms or campsite assignments:
. . . unless occupied, the Front Desk CM can usually change/exchange any room (within the same classification)
. . . if you do not like your room or location, typically it can be swapped with someone else's room
. . . yes, the other person, checking in later, gets the worse room, but you frequently get the one you like
. . . about the only exception is trying for a handicap room when one is requested by someone else
4) Not only does the Early Bird Get the Worm, they also get the Better Room/Site.