Can you solve complex quantum physics problems given plenty of time? I'd guess not (if so, please pick any other complex topic you have no knowledge of). The PCs are not super-geniuses that can solve any problem given enough time. In the case of a secret door, you could have overlooked the trigger, or manipulated it incorrectly, and not be able to figure it out.Sure if there is some special key or pattern sequence that searching the rest of the dungeon would reveal and cause an “aha” moment, exploration-oriented players love that. But unable to open it based on a failed skill check when they have plenty of time...?