if they say escrow is closing on the 28th, how early can i move in?

Answer 1

You can movew in on the 28th, the day escrow closes.
Now if the house is vacant you could ask the seller if you could move in earlier at a prorated rent. Most will not let you due to insurance reasons, or incase the loan falls through last minute.
If they do let you, most likely you will have to sign a hold harmless by the seller so he is not liable for any damages to you, or the home.
Good Luck
RE Agent,
Remax

Answer 2

About an hour after closing. As soon as it closes it is yours unlees you have agreed to let the seller stay for a while.