I have used a different method for self bondage and it really works. I put myself either in a crib or a high chair. I am locked in so as not to be able to stand up or get out. The keys to my confinement were attached to a nylon cord and then placed in a plastic cup and secured to an electric rotissere motor shaft directly above me but out of reach. The open top of the cup facing upward. The motor was then plugged into an electric timer and I set whatever time I wanted the motor to start operating. When the motor gets the power, the shaft rotates slowly because it is a geared shaft. As the cup turns 180 degrees, the keys and cord fall out directly over me. The looped cord assures that the key is easily reachable even if the key drops away a bit. If your diapers are covered by overalls or a panty girdle or anything that requires you to get those off before you can get to your diapers, then only the arrival of the key will allow you release.
In fairness, you also have to be aware of some possible issues. If the electricity gets interrupted, you will be on hold longer. Because it's self bondage if there is no one close by, you need to consider fires and earthquakes and severe weather as possible hazards. Safety first and then apply what you are comfortable with.