If you have handcuffs use these Else use some Chain and a padlock.
Freeze the Key into a large solid block of ice. Once it id frosen solid put it into a large Bowl.
Strip naked and Find a place Where you Can lock Yourself up, like a radiator, by one Hand with the Bowl next to you. Now you have to wait for the ice to melt before you Can unlock Yourself. The duration Depends on how Big the icecube with the Key inside is.
Dont have Anything Else Then the Bowl within reach so that the time Will feel even longer as you have Nothing to do except waiting for the ice to melt.
If you want it even harder you Can lock Yourself in a position that Will become painfull after a While.
This type of self bondage Can be varied in countless ways from easy to extremly hard and painfull.
Ok so I don't want to make an example of you and English is obviously not your first language but it needs to be said this is a BAD idea.
There is no safety escape in this plan at all, if the house catches fire, if he has a heart attack or indeed if any number of any other emergencies happened he is stuck and could die.
Any time you play solo with handcuffs or chain and locks you MUST have a spare key where you can get it in an emergency. If using ropes then safety shears or scissors.
Self bondage can be fun but it requires a high attention to safety, you are the only one who can save you if something goes wrong.