Right now the O3 portal lasts forever (i.e. until server reset). But I don’t see why this is necessary. Any necessary preparation, such as checking the players with Runes are still there and no-one else is missing, asking any players not up to it to leave, can be done in a couple of minutes. What it does do is encourage toxic behaviour, when e.g. some random group of players claim it is their ‘private’ O3 run and everyone else should leave, and refuse to open until they do.
Contrast that with the WC portal. With it disappearing after 90 seconds if anyone wants a private WC they have to persuade anyone else there to leave/not join, whether by bribing them or being nice. Rarely happens now but I’ve had it happen in the last year – two people wanted to do a WC together so asked me to leave and I did.
So have the O3 portal time limited too. It should last longer than the WC portal as it needs additional organisation but not much more. If the timer runs out without all three Runes being supplied then it vanishes and everyone gets their Rune back.
Does that mean undesirable people mught get into ‘private’ O3 runs more? Sure, as there is no such thing as a private run. If they are not good enough they won’t last long anyway. Or the people with the Runes can use them another time.