IIRC, the standby is there to protect the tubes from something called "cathode stripping", and therefore extending tube life. I've always been told that if the amp is not used frequently, the consequences of not using the standby are negligible. FWIW, both of my 70s Orange 120 heads came from the factory without a standby - as did most Oranges from the early days. Also, I rarely use the standby on my '72 SVT, and the original Magnavox-branded TungSol 6550s are still in very good health. YMMV
One thing I HAVE always done whenever possible is allow the amp to reach room temp before turning it on, and if that is not an option, let it warm up in standby mode.