Another (complicated) way would be to use BIP 65 And create a CLTV transaction.
You can give him the private key to the address that holds the output, and he can't spend it till the specified time has elapsed.
The downside of it is that it's permanent and you can't undo any mistakes or spend the funds later of you wished to.
You could use BIP 112 instead to make a CSV transaction that can be invalidated in the future of you ever change your mind.