Yes, you can clear out of order. but there is a paper trail. the PALL list (standby) lists all S3-S5's based on seniority, everyone else is time of check-in (imagine that!!!). The list also has revenue passengers, and I find it easier to do it manually (GA1,2,3 etc - number being the line # on the list) while others do GALL and spits out BPs for everyone.
I have been the gate agent and have had this. I will call the more senior passengers to the podium and explain I have a family / group and want to seat them together, and if its OK I do that, and here are the seats I can offer them. I'll also sometimes print off a seatmap so they can select their own seats (GA1/18F, for example). Most of the time the passengers are OK with it... but I've had a few sticklers...
I would do it at the 30 minute cut off, but I have a different way of doing things. I assign a dummy printer to save time & boarding pass stock (GAXXX) and if its wide open, i give everyone their seats and let them board with their respective group. If its tight, I'll still clear the list to protect my NRSAs but not hand out seats until 10 minutes prior, in case someone shows up at the counter and they let them thru... this way I still give the revenue passengers the best seats available.
I think we will have something similar to the US-East system that mixes it.
I'd like to see S1/S2 based on time of check-in, while S3/4/5 remains DOH. this way it puts value on my S1 passes. S6-9 will also be time of check-in.