Well, if your private keys are leaked / cracked then no amount of locking will help. On the other hand, since this sort of locking would be client-side only (ie. the blockchain can't and won't enforce it) an attacker can just change the system date to a month in advance and voila.
Perhaps a better solution would be for us to write a little function that uses the nlocktime equivalent in Monero to send the funds back to yourself, but this is "dangerous" in that the funds are not recoverable even in an emergency. They are well and truly out of reach.