I think there is a proper test for this:
Every five min after you've done your shot, you have to drink a litre of water. When the water stops squirting out of the hole where you did the shot, you know then that it's safe for you to enter the water.
The accuarcy of the test can be improved by you standing on one leg when drinking the water and you can also add colouring to be able to see the jet more clearly.
Give a try and let us know how you get on.