I understand where the OP is coming from but this may be an area when "it's a computer game and this is what needs to drive how stuff works."
If you have played Fallout 1? It had a mechanic that if you did not bring back the water chip to save your vault and if you did not do that by X date & time, game over, Man.
People hated that because FO1 was very sandboxy so you were encouraged explore everything and I believe then nerfed the clock running out in a patch.
I think trying to have a clock run out in a CRPG is just a bad idea. It can work great in a single adventure where the DM is upfront that the clock is running but I would never try to build a whole campaign around that.
