The last time I can recall the park opening after 10am was for Fright Nites 2003, when they did 11am-11pm. Still, a long time ago!
In any case, it's been a long time since the park did a passholder day, so it's lovely to see them do one again. The thing with these sort of days (ie ones at the start of season) is that the money they don't earn from standard entrance tickets is sort of recouped by the fact passholders tend to spend more than average on their first visit of the year due to new merchandise. Plus, it helps bring value to the annual pass (despite it already being great value) and added satisfaction. So it is win win.
A 7pm close giving the opportunity for a dusk ride or two is a lovely bonus too, and it's good to see the park continuing their experiment of offering later closing times. Hopefully that can continue.
I also agree about Fright Nights: it would be interesting to see the park explore 11am-10pm at the very least. I don't know how realistic it is to happen, since one of the things that ties the park's hands is the number of under 18s working at the park. Equally, the park simply seem to have veered away from running rides till 10pm: they don't even do it for buy outs or their VIP/Press events. But it would be interesting to see.