[Amps] filament tube life, turn on's and time on target

[Artmouton]

I have an MLA 2500 with, what I hope is a lot of tube life.

I mostly work CW DX (now mostly restricted to 80 & 40 with band conditions)

Unlike 20, etc with a beam I am finding it more and more necessary to use 
the amp to get through (inverted Vee at 60').

Am I right to be reluctant to turn on the amp just to make one dxcc band 
contact, only?

Knowing the finite life of a tube and the price of the ones in my amp, I am 
quite reluctant to just turn it on, make the contact, and not use it again 
that day.

Any feeling in the group what difference in tube life that makes?

The timing circuit is working so I have the usual delay from filaments on to 
transmit, but, just the idea of the filaments being turned on and off 
worries me.
Thanks & 73,
Art K5FNQ