time on your hands

We phoned for a plumber and one arrived at the double and fixed the leak in no time.

if you go somewhere or do something at the double, you go there or do it very quickly 

Two surgeons arrived in the emergency room at the double.

If you have some time on your hands over the holiday would you mind helping me with the garden?

 If you have 'time on your hands' it means you have time to spare.

 a period when you have nothing you must do 

You must have a lot of time on your hands.
あなたも暇だねぇ。

These kids have too much time on their hands, and they get into trouble.