Site works - how wet is too wet?

Our builders started on site a couple of weeks ago, which was very exciting, and they had a pretty good schedule lined up - site cut & fill, piers, then plumbing to be done last week, slab scheduled for end of this week. Sadly, due to the weather, the block is very wet so they haven't been able to do the plumbing, so we are at a standstill until the site dries out a bit. Weather forecast for the foreseeable future doesn't seem too favourable. What experiences do people have with wet sites at this stage, how dry does it have to get before work can recommence? I'm having visions of being stuck at this point for the rest of winter!

if the earth is wet then its harder for them to drill holes for the pierings
Piering needs to have time to dry itself and be solid but in wet condition, it is not recommended to pour the piering.
I think it is harder to do earthwork when it is raining
Slab in the other hand, can still be poured in "light" wet condition, a slab cure better when wet, it get stronger.

Thanks Avalanche, guess we'll just have to wait for it to dry out, the builder has said the main problem at the moment is its too wet to get a digger in to do the drains, but once that can be done we should get back on track!