How long 120mg. well, the half-life of methadone can be up to 59-hours, so after 2 and half days you would still have 60mg's in your system. But this doesn't take into account multiple doses.
A third type of lock is a security lock. This lock is like a typical password, to prevent someone other than the owner from using the phone. If activated accidentally, the user manual or carrier customer service can usually tell you the default code.
Open the Settings app on your iPad and select General. Then look for where it says Passcode Lock. Tap on that and disable it. You also want to make sure the Simple Passcode is turned off. After that you can go back to the General screen where you might also want to switch Auto-Lock to Never.