Can anyone suggest a way to take a water hose with the pressure truned on, and have it begin to spray at a predetermined time? I am trying to set up a situation where someone gets wet if they don't complete a task in the alotted time.

They make timers that will control yard sprinklers and such. You might take a look at those and see if you could make it do what you want. You can find them at Lowe's and Home Depot.

You could also buy a simple light timer that plugs into any outlet and then plug in a small aquarium pump. This way you could limit the amount of water that would be sprayed.

When I do a Google search, I find timers that will schedule your watering, but none seem to have a feature where you can set the timer to begin watering in 3 minutes, etc.

An industrial supply company such as Grainger should be able to hook you up with a dry contact timer and a 12-volt solenoid water valve for less than $100.

Keep us posted...