I don't want you to fail. I just want you to enjoy teasing yourself with what you can't have. The same way my Mistress makes me.
If the vibing gets too much, stop and pause the clock to cool off, then run down the rest of your time once you've regained control.
Don't wait for me to tell you to unlock. Once you've done your four hours, take it off, clean it and yourself and then the next rest period is five hours. Can you see the pattern here?