I believe turning the tubed device off for a short listening break (such as the few hours referenced) will not contribute to the overall life of the tubes. I think/believe it is better for the integrity (physically) of the tubes to remain at a relatively steady state and temperature versus cooling off and heating back up.
Additionally, with a lot of tube equipment that does not incorporate a soft-start type of approach for the tubes, it is my belief and understandinging that the turn on process is more wearing and a greater risk to the tubes than leaving them on for a mere few hours.
In such a case it would be my advice to leave the equipment running for a good portion of the day versus turning it off and back on. But please note that I am not a tube expert but have over the years owned some very good NOS tubes that I paid a fair amount of money for.
Additionally, with a lot of tube equipment that does not incorporate a soft-start type of approach for the tubes, it is my belief and understandinging that the turn on process is more wearing and a greater risk to the tubes than leaving them on for a mere few hours.
In such a case it would be my advice to leave the equipment running for a good portion of the day versus turning it off and back on. But please note that I am not a tube expert but have over the years owned some very good NOS tubes that I paid a fair amount of money for.