The spawn timer isn't actually random, It has a spawn timer of 60 minutes from the opening of a new instance and 90 minutes from the previous Dalriada ending. These timers are reduced by clearing Skirmishes/Critical Engagements so in a fully active instance it's usually like 35 minutes give or take (although these days that's less common of course).

When it comes to actually clearing it the echo buffs you get from being below full raid size are pretty substantial and make small parties actually kind of a cakewalk. I've cleared it with 4 people before without any issues. Obviously it's going to be a bit tougher if your party is all first timers without any of the mettle buffs/knowledge of the mechanics etc but overall party size isn't that much of an issue at least. If you can find a couple of like minded folks trying to clear it you should be fine there at least.