You would be surprised how long the tarps keep the roofs from leaking. Most of Orlando was covered in tarps last year after the hurricanes. I waited until May before I finally got my new roof.
My parents in Destin rushed to tarp their roof as soon as Ivan ended last summer. Their roof is steeply pitched and my father rigged this elaborate pulley device to get their tarp in place (very ingenious fellow my dad). Had a heck of a time and put himself in much jeapordy. Bless his heart, he worked so hard on it all day long. The next morning the Fema people came into their neighborhood and did all the neighbors' roofs in a few hours. Be careful though. The fellow across the street from my parents had a tarp put on their roof and it turned out that they really didn't have enough damage to warrant a new roof. His insurance company wouldn't pay, but he had to buy a new roof anyway since all the nails from putting the tarp on caused so much damage.
I am in Winter Park and lost a *lot* of shingles in the hurricanes last year - my roof was old, but we had a double layer and we were not leaking after the hurricanes. FEMA came out and could not believe we were not leaking. We we happy to get a blue roof...but then the roof did start leaking, not a lot, but enough to cause some stains and consternation! We got our new roof finally in May as well. How nice to not watch the ceiling for new spots every time it rains!