When transporting your vehicle, there is waiting involved, whether it's for your shipping company to find a carrier or the carrier to pick the car up.
You will spend time simply waiting for everything to happen. The term "transit time" is how long it will take for the carrier to transport your vehicle from City A to City B - IE, how long he is in transit.
This can vary depending who you are shipping with but more importantly where you are shipping from and to. Typically the further you ship your vehicle, the longer the transit time will be.
Coast-to-coast auto shipping is usually anywhere from 10-14 days, depending on the route that it takes and how many other stops there are along the way. But the term transit time simply means how long your vehicle will be on the road.