In the original, that was when true seeing spells/effects, wands of secret door and trap detection, etc would be brought out!I don’t think that’s gonna work for me, since that leaves open the possibility of making the tomb impossible to complete.
Of course, if you run out of charges, or have your high-level cleric or illusionist die, then there is the possibility of non-completion. That is an aspect of Gygax-style "competitive"/"skilled player" RPGing.
I don't have think I have much advice on how to make this work in 5e, sorry. I don't think that ToH is a great venue for "rescue the prisoners"-type scenarios (which would make time matter). You could go with no retries, but then if the players run out of options they have to probe the aether for an answer (a type of deus ex machina) which triggers an encounter with demons as per the module, and when they defeat the demons the demons give them the answer/info they need? You'd need to tell the players up-front that probing the aether is a thing, but a potentially dangerous/costly thing.