It could very well be that 24/7 operation with a Class A biased amp like the X250 is ultimately cheaper than turning them on and off, as the amps will be much less likely to break and require expensive repair. Keeping the amps on 24/7 means that they will not experience the relatively severe thermal cycles that occur with Class A amps when they are turned on an off. The heating up and cooling down that occurs when you turn a component on and off wears down internal componentry because they expand and contract as a function of the temperature (the most frequent analogy is what the winters do to highways in the Northeast), all the more so with a Class A biased amp, because they run relatively hot when they're on. Running X-600's or X-1000's continuously would likely cost a fortune in electricity (and make for damn hot listening rooms), but if your X-250's only burn 270 watts each, it's probably smart to just leave them on.
I'd love to run my Class A biased VAC monoblocks 24/7, but it would prematurely kill the output tubes.