How far over the limit can I go

Better safe than sorry. Pay to play.

Have the same set of tubes in my CAT preamp since 2016, about 10,000 hrs. Still going strong. (Mullard 12AX7 reissue, Reflektor 6922). 

The answer is they could fail tomorrow or not.

Oh the joy of tubes.

Was just listening to a copy of Joni Mitchells "Mingus"I picked up earlier today.

Last track on side two.

Distortion.

Thought I had a bad pressing.

Lifted the arm, played the last track again to see. 

Left channel dead.

Checked to see if I had pulled a speaker wire or an interconnect - was moving gear around.

Then I noticed the lovely glow of an EL34 that was red plating.

Ugh...

Thankfully, I had a back up set of tubes ready to go if something failed.

Had a set of Winged 'C' tubes that lasted forever a bunch of years ago. These Gold Lions I've been using have a terrible failure rate, as do the Psvane EL34PH replicas that I bought a couple of years ago.

Sound wonderful! Just don't last...

Basic Tung Sol EL35B as back up.

Next set of tubes will be the Winged 'C' again.

So yeah, your tubes could fail tomorrow, or not.

If, there is a risk of a cascading effect from a failed tube, then see if there is anyone near by with a tester and check the state of your tubes.

But, a back up set is always a good idea. A little inventory can't hurt.

That ARC hour meter is a cool feature.  I’m left guessing with my tube gear.

I would contact somebody like Upscale Audio or Brent Jesse let them know what type of system you have and the tubes you are currently using and let them recommend some NOS tubes not only will you be replacing your tubes but you will also experience a much better sound. Good luck