As long as you clean them to make sure that there hasn't been any "growth" in the week, they should be fine.
I regularly use dailies as fortnight-lies / monthlies. It's much cheaper and as long as you make sure to clean them properly, they're also way more comfortable. The longest I've ever left them and come back to them though has been 2-3 days, so if yours feel at all uncomfortable etc, then don't wear them.