Undaunted delve dailies don't force delve boss to spawn.

Contraptions

What the title said. Compared to the Orsinium delve quests, the Undaunted delve quests take much longer to complete because more time is spent waiting for the delve boss to respawn. I recall the devs mentioning that if you had a quest for the delve, or if you needed the delve boss for first time completion, the boss would be forced to spawn within 20 seconds or so of it being killed. If not, the respawn time would be around 5-10 minutes.

I don't have any proof of this, but anyone can grab a delve quest (preferably one that sends you to a delve that you have already cleared) and go to the boss spawn area. You will see that you may have to wait a few minutes or more before the boss appears again. This should be fixed. The dolmens now spawn faster thanks to the new FG quests, so there is no reason why this should be any different.

AGrz5585

I did one that I've already completed before 1T. Bossed spawned as soon as I entered room

Contraptions

Could have been you entering the room just when the timer ended. Just completed a quest where I had to wait few minutes or more.