Hi Saima,
Just curious--what is your aversion to the waiting workflow? One concern I have is the performance of the system if you have too many waiting workflows. The scenario where a workflow deducts from the duration each day seems feasible, but it also seems like it would create a lot of workflow tasks each day--it's hard to say which is worse!
If I were staying within the application's toolsets, I think I would go with the waiting workflow, personally. However, if you have other options available to you, you might consider an SSIS or Scrbe script that runs nightly or something of that nature to continue with optimal performance.
I'd welcome others to chime in with their opinions as this is an interesting question!