How long does it take your tube amp to warm up?

At least an hour for my Quicksilver Mini Mite mono blocks to reach their best sound. This is with regular use. If they sit for awhile it could be several hours for them to sound their best. 

My NYAL Futterman OTL3s, converted to triode with eight 6LF6 tubes take about 20 minutes of warming up while playing music. At 40 minutes they lock in. 

I’ve tube mono’s and a tube preamp. I’d say at least an hour to sound it’s absolute best!

To my practice, solid state amplifiers need more warming up time than tube ones. I have two of them, one push-pull with 12 tubes and the other SET with four tubes. In a few minutes they sound good, while my class D solid state amplifiers need a few hours to get closer to the best. 

Does anybody know if tube amplifiers with speakers hooked up but without any signal can stay powered on without harming them? Many years ago I got to know a very nice guy from Boston area. He was then a Thiel dealer, in particular. I was excited then with new Thiel CS 3.7s. I lost a contact with the guy, but this is what he told me. 

Tubes undergo less wear when not under load so will last longer, but I don’t think any manufacturer would recommend leaving them on: fire hazard and a really short tube life.