Solving mysteries is a balance between accomplishment and frustration.
It's it's too trivial or it's inevitable then it's dull. If the players spend too long frustrated about how to solve a mystery without making any progress than the game bogs down and any feeling of accomplishment inevitably becomes anti-climactic.
So you can partly solve this if you are on a timeline, and failure changes the situation for the players (generally makes it worse) - but still, the players have to have the sense that they could have solved the mystery, or it just ends up playing out like the GM dicking around with them, wasting their time for no good reason.
If you allow for no degree of editing once the situation has been set up then you are putting an awful lot of pressure on yourself to get it all right in prep.