Question about valves running hours

Thank you all for your comments. 
My amplifier is a push-pull from Cayin. 
When I bought it, the lady in the shop told me to run it for periods no longer than 7 to 8 hours due to the heat. And to wait some time before turning it on again (I understood waiting around one hour or too, but maybe some minutes are enough).
I couldn't ask for more details because her English was poor and I don't speak Chinese! I'm living in China...
So now I'm just trying to get your thoughts about this matter to better understand my amp. 

That makes no sence at sll. I recently bought the Excellent Jolida 
Fusion 3602  integraded amp.with a bunch of of upgraded parts including the Excellent 
Rike Audio paper oil capacitors that take 300 hours to break in.Check out their Amplifiers  $300,000+.
I have used Vacuum tube gear for years as of today I have been running this Integrated amplifier one week straight 24-7 with 
Vintage  output and phase splitter tubes, the second week changed out the EL-34 tubes  input tubes after 175 hours ,and installed KT- 150 Vacuum tubes just flipped a switch on back. Factory stock tubes are guaranteed for a minimum of 1,000 hours of play time.Vintage tubes many times that .
If your amp is built correctly it should have a stand by circuit, as well as a slow start so a surge  of voltage doesn't shock the tubes on start up.
Also manual bias of the larger input tubes is much more accurate 
Way of biasing the individual tubes ,auto biasing has a bunch of resistors to average the circuit which in turn takes away a bit from the accuracy a bit overall.this several engineers Have said as a purist approach. 

My work system is driven by a 55 year old Masterwork amp (by pilot).  I use it for 8 hour work days all of the time and it never fails me.  It does get hot but I make sure it's well ventilated.  If this amp can take the abuse without ever burning up tubes or caps, why can't a new one? 

To further clarify. Like myself I wanted to completely runin the circuit
And left on for 300 hours non stop. My amplifier sits on top of rack 
And heat is not a issue tubes are made to dissipate heat mainly from the Larger input power tubes with no issues,or danger.any quality 
Amplifier has safety circuitry between the digital circuitry,as well as fuse. Good power tubes you should get at least 3,000 hours . My smaller   preamplifier tubes all are Vintage  1950s
Vintage tubes on average at least 10,000 hours possibly much more.
Onot any amplifier brought into the U.S check for U.L approval  . If not it has not been  verified and Electrically approved.if bought on Ebay 
Verify before buying. In Europe EU  approved.in the U.S you cannot Legally sell  without it ,or face $$ liability if something happened !!

Migueca, I do not want to alarm you, but it looks like the Cayin is of Chinese origin?

Several years ago I purchased a Raysonic sp120.
Designed in Toronto, built in China and CSA approved.

Turns out the power transformer was not really rated for 120v

This elevated the heater voltage and caused the tubes to fail early due to overheating. My expensive Gold Lion Tubes failed after 3 months

I did talk to Raysonic, but they refused to acknowledge there was an issue.

I had it fixed for $300 by an excellent tube technician and it sounded so much better and the tubes lasted almost a year after that - played 8 hours daily

I would have the amp checked by a good tube guy - could save you a lot of money in tubes alone.

Now I know some will say a lot of gear is made in China and works fine.
- mine is just one of a miriad of tales about kit made in china that was less than perfect.

The SP120 was my first a last tube amp, so I was pretty green - in more ways than one.

As for the 8 hour limit, I’m with most others opinion, turn off when not in use - you’ll save on hydro

Regards