This sounds like a bugged queue, but I had this sort of problem in 2013, when the game was fresh, in Sastasha too. I think me and my mate waited like 180 minutes for Sastasha until the point we turned off the game and ranted a bit why there are mandatory dungeons to the story. There comes a lot of different problems together, and this can make it even more difficult to get into a certain dungeon:

1) Bugs. They happen.
2) Very low population - as a Red Mage on my own, I wait more than 30 minutes. Realistically, it's up to 45 minutes on primetime on my server. Now this can exponentionally go up depending on how off your local time is compared to the prime time. When I was server hopping until I found my beloved Zodiark server, I was on Ultros - an U.S. server without knowing. As European, it was of course dead when I played.
3) When you queue for a specific dungeon, you always take longer than a Roulette. I think it might be because the game builds a team around your needs while a Roulette you are filled into a random Duty. This way it takes longer. You might have seen that e.g. the tank shows 1/2, and suddenly it's 0/2 again. Healers and DPS the same. And you wonder, why this is happening, why would the game deliberately take away matches that you desperately needed. It's because they are filled into a fitting roulette. It's like a friggin dexterity game, and some of the balls (player) jump out of the holes (your team) and land elsewhere. It takes ages to have 2/2 tanks, 2/2 healers and 3/3 DPS with all this juggling, almost like a slot machine that never matches until you hit the jackpot.
4) Constelations of the roles. Imagine, you are the last DPS spot. The party is almost formed, just one healer is missing. Now a healer is actually registering for a duty - hooray! But wait, he is premade with a DPS. So he is not matched into your party, because the DPS spots are full. Now imagine the same with a healer + tank, 2 healer premade, 3 DPS and a healer, etc. There might be 15 healer and 12 tanks ready, but in constelations not suitable for the current matchup as they bring their friends and those would exceed each role. So the matchmaker assigns them to different dungeons, basically starving your queue. Until the point you have a single healer - like me - registering for MAIN SCENARIO DUTY, the tanks have been matched away already. And I leave the queue or get assigned elsewhere after a while to keep my waiting times lower.
5) On top of that, I personally do rarely register for MAIN SCENARIO ROULETTES myself, so while I am participating at Roulettes, I systematically prevent myself from being put into Praetorium, despite I am in Roulette, a single healer and ready to heal trough whatever instance it might be BUT those two main scenario quests. As they take long, many players rather do the other duties and then log off.

In short: A big chunk of awful problems are in your way. Once you are trough, ironically, it gets 10 times faster for the future visits of each instance. I waited ages for Bismarck as Scholar (!) when I had to do it and specially requested a Duty Finder queue. Now I instant-pop it on Roulette.

Sincerely,