Won't be much use if it times out.
Can you not run your computer for longer spells....18 hours doesn't seem much, you ever tried Climate Prediction

Perhaps you could set your profile to just Dengue work units, they seem very short at the moment.
On my rig they have an ETA of under an hour

As Didactylos said, tasks have deadlines that allow for interruption. There are two Start Here forum FAQ's that will give some more relevant information:

1. The deadlines of the different WCG projects: http://www.worldcommunitygrid.org/forums/wcg/viewthread?thread=17160

2. The Checkpointing explained (to allow resume later, from where you left off): http://www.worldcommunitygrid.org/forums/wcg/viewthread?thread=11332

cheers