If you ate mold on bread and you are allergic to penicillin how long will it take for it to go into affect?

You should be safe: There are many mold species that grow on bread, so the mold may not even produce penicillin. Also, the amount of drug in the mold is relatively low. If you theoretically ate a large chuck of penicillium mold and are allergic to penicillin, you would notice symptoms within minutes to an hour or so. Note: most people told they are "penicillin allergic" are actually not. See your doctor for more info.

No issue: Of course, you should avoid eating moldy bread. But even if it is infested with penicillium, the amount of penicillin from it would be too minute to cause an allergic reaction.