I have a leak in my hot water expansion tank & unfortunately has come onto my ceiling, can I turn it off until I get somebody out to repair it & how do I drain it? Also what then happens when my hot water (gas) timer is on to heat the water up?

I have a leak in my hot water expansion tank & unfortunately has come onto my ceiling, can I turn it off until I get somebody out to repair it & how do I drain it? Also what then happens when my hot water (gas) timer is on to heat the water up?
This will depend on which side of the water heater shut off the tank was installed on. (see image). If the tank was installed on the heater side simply shut the water and gas off 7until repairs can be made. However, if the tank was installed on the pressure side of the stop the entire house must be shut off at the house shut off to make repairs. Good luck. Tom

Thanks Tom, much appreciated.