I run mine 24/7 - have been for yrs - unless I'm out of town. I feel it sounds best with a day's warm up. It has to do with the class A Mosfet outputs - that need to be at max temperature to sound optimal. That's the way they are designed (I have some other class A amps that are the same). Schiit designed the Lyr/Lyr2 to use the case as a heat sink - unique as far I'm aware for a class A amp. That's why the case and vol knob get warm. Best to use some kind of footer underneath to raise the Lyr a bit higher for good airflow. I use Stillpoint mini risers - that also act to damping ambient vibrations from reaching the amp.
You are right in that the run time will effect the life of the tubes - I look at it as just the cost of ownership. I suppose you could run a cheap backup pair (stock) and swap before a long listening session. The tubes themselves heat up pretty quick - 10 mins.
PS These Symbio P-1s look pretty 'cool' - I have
not tried them