You should be able to get away with a few days to a week if the log is off the ground and in a protected place. The longer the bark stays on the better chance of bored but also rot getting into the wood. It is the job of the fungi to break down wood and in whitewoods it doesn't take long to get infected.
I use spray shellac to seal all wood staves, backs and ends. It is easy to use, seals well and easily removed later if wanted. Others use carpenters glue(TB, Elmer's, etc)but they are harder to remove later. Some folks don't seal whitewood backs at all and generally with good results. For me it ain't worth the risk.