However, an REO contract will typically modify these terms somewhat, so you'll need to read any counter offers or addendums received from the bank (and signed by you) that would provide different time frames than those that were indicated on your original contract.
There is no law that states when a loan needs to be funded - you'll need to follow the contracts that you signed.
Are you asking how many days, by LAW? In Arizona, and to my knowledge in every state, there is no law that dictates a deadline for obtaining final loan approval. That is a contractual issue, depending on the terms of your purchase agreement. Are you the buyer or the seller?