When do you turn off the tubes?

Having had recent surgery and spending a lot of time at home, I was wondering how long a break from music do you feel you need to be taking before turning off your tube amplifier.I could leave it on all day even when not listening but that would be 12+hours/day.While my PrimaLuna Dialogue HP is gentle on tubes, the thought of retubing 8 KT150s is an expensive prospect.I usually turn the amplifier off if I am not going to listen for around 3 hours.What do other people do?

On for 20 mins before. Off when done. 

Always turn off tube amps when not in use or near future use. No reason to leave them on they voltage stabilize within mins and with the heaters warm up in 10 mins or less. really not worth the tube wear or power use if not going to be used in the near future.   Tube amps have 100's of volts on the plates some are 1000v+ so really do you want that thing on all the time when your not home.

Also don't leave them on when no one is home not really that safe, I've seen tubes self destruct when they fail be nice to be home so you can turn the thing off so not to damage other parts of the amp, or burn your home down. you wouldn't leave your stove on when your not home would you?  

 I feel its irresponsible to leave equipment on all the time just to say oh I don't like to wait until it warms up. well the planet is warming up so take a few mins to plan ahead when we listen. Turn things on go get a drink hug your spouse your kids what ever then go relax and listen.

if your really savvy get a remote switch to turn them on when your on your way home.

I never leave it on when away. Just wondering about the 1-2 hour breaks.
Yes if I am listening to music and say turn the TV on to catch a show or game or something I will leave it on because I plan to listen after. Or in the case of a game during if it's not going well. :)
For an hour break, I would leave things on.
When I go to bed, everything gets turned off.