Yes, you can leave them on all the time. The only disadvantages to leaving them on all the time are faster tube wear, and higher energy bill. It is probably better for the gear to leave it on all the time, rather than heat cycle and current surge at turn on, though in your case Belles would have designed those liabilities out.
If you use exotic expensive vintage preamp tubes then it might get expensive to replace those every year. Probably need new preamp tubes after 1year of constant on, depending on the preamp design. 1 year is 8760 hours. Signal tubes typically last 2000-5000 hours. I could not find detailed about the VAC preamp to see what tubes it uses.
I switched to SS because I want my system on all the time ready to play with touch of the app. I hated realizing hours later that I left the tubes on. My SS amp has sleep function on no signal.