300Bs - does leaving them on shorten their life?

Some equipment has built in protection.

My Cayin  tube Amp has a 30 second delay, test and I suppose you could call it a soft start.

My prior McIntosh SS amp has a test/delay protection sequence.

My Adcom ACE-515 power enhancer (not a power conditioner) power controller (in my office) has a time sequenced 10 sec turn on delay for the amp; 30 sec turn off delay for accessories. (prevents thump to speakers).

tempted to turn on and leave on all day. Instead of powering up and down many times. 

Correct answer depends entirely on what you mean by "many times". If you mean many times a day, the greatest most intense stress is the thermal expansion going from off to on. This is why some designers like Herron incorporate slow warmup circuits. Greatly extends tube life. 

But if "many times" means one time a day? Well then look at it this way. Let's pick some arbitrary numbers and say tube life just sitting idle is 5000 hours. At idle. Playing music uses more power, tubes get hotter, wear faster. Let's say you crank that thing full blast all the time. Tubes last 3000 hours. Just throwing numbers out to get you thinking in terms life and wear. Though these are probably in the ballpark. 

Okay so now every time you turn them on from cold, that flip of the switch is something like at least an hour of running idle. So if you are turning it on and off 3 or 4 times a day then probably better off just leave it on. And that's how that works.  

https://www.youtube.com/watch?v=P7WkFEVbxu8

https://forum.audiogon.com/discussions/tube-failure-what-would-happen-in-worst-case

go ahead, leave em on, walk away, don’t worry be happy

i appreciate all the comments.  I think I power on and off 3 or 4 times a day. Today will be 5.  I sent an email to VAC to see their thoughts on it.  Replacing 8 300Bs is a pricey move that I’d like to put off.