tube amp storage

My question is how long can a tube amp sit unused before you would need a variac or slow turn on method to turn it on? To be clear I am asking specifically about a newish Jolida 502P
I really don't see a problem here. I could be wrong, have been before.
By my experience several years has never been a problem with tube amps, large and small.
I do not think there is an exact number, but it is better to be safe than sorry.
Doesn't the 502p's "slow start" feature take care of that issue? And also, I'm sad you're planning to not use the amp...don't you care about all the people out there who don't have a 502p to not use? It's just unfair...*sniff*...