I thought the main story doesn't give a sense of urgency because of the tadpole is basically dormant.
Make it so your party members starting to turn into mindflayer, one by one, if the player takes too long in the quest (or x amount of quest/rest). Eventually, you will turn into one yourself if you basically take forever doing ever quest.
With that said, give them the option to go back and finish their quest. Just don't allow players roam around and ignore the padpole completely.
When you force urgency people skip everything but the main quest and then kvetch about difficulty and how they have to go level up but can't because their head's going to blow.
I dont want rushed. Tadpoles is for many, we can breathe a bit. I WANT to do those side quests. I want that xp. Sorry you want to finish the main quest in 5 hours.