Normally the greeting you mention is constructed by Unity when a custom one is not recorded for the active greeting on the handler in question (i.e. the opening greeting in this case) - I'm not sure how you have your call routing/handler links laid out so I can't really speculate much beyond that - Unity isn't going to play a system greeting and then also play a custom greeting for the same handler so I'm guessing the after greeting action on the opening greeting is going to another handler which is playing the greeting you want. I suspect you need to force the after hours greeting to be the "blank" radio button so it falls straight through but that's just a guess at this point.
Yes, at some point we'll circle back around to specific holiday greetings (and vacation greetings for subscribers that expire on a given date automatically and a few other related items) - just a lot of stuff on the queue and not enough bodies to cover it all. Your best bet is to ask your account team to stick a PERS request in for this so the product folks prioritize the work higher.
