Is there blood? Do you see any notable difference in the way he walks? or the way he is acting?
The picture is blurry but the break doesn't look as bad as it could have been. In simplified terms, a turtle's shell serves the same purpose as a bug's exoskeleton. If the break is complete the vet may wire it shut or they may even use super glue. This is still what most would consider an emergency, so if you have the cash then please take him in sooner rather than later. Monitor his behavior overnight. Note any changes and take him into the vet right when they open tomorrow.
If you notice any oddities in his behavior, then please take him into a 24 hour vet. Otherwise, I think he will be okay until the morning.