I am planning a pseudo Ravenloft campaign for 3.5. The campaign will feature a fairly short, open world style, main story arc along with a good number of side quests/arcs.

I want to add a mechanic that creates a sense of time pressure while simultaneously giving players enough time to explore the world.

My current idea is that enough time in the Dread Realms can inflict the PCs with a soul sickness that deals Cha drain and, if it reduces Cha to 0 traps the PCs soul in the Dread Realms forever. Good deeds/a special type of item scattered through dungeons can cure, reduce the progress of, or otherwise slow the soul sickness.

However, I have never used a mechanic like this before and appreciate any advice or alternative ideas on how to add limited time pressure to my game.