Do you mean S Type or FTRS and do mean mean your friend wants to terminate early or that the Army wants to kick him out? If it's FTRS and your friend wants out then the normal rule is 6 months notice to terminate a contract early. As with all things his best bet is probably to approach the chain of command explain that he wants out and ask what the earliest he can be released is.
A quick google of 'FTRS termination early' will get you the relevant DINs. They are all open source.