It could be more difficult, but lots of parents work nights and evenings and have custody. If he has child care available, it's a non-issue. Or, for all we know, he may have the ability to switch to day shift and only chose to work evenings because it meant that he and ex didn't need to pay for child care. Switching back to days and hiring day care would solve any problem.
So he needs to think about child care, but other than that, it shouldn't be a big deal.
Its not just about child care.
When you have two fit parents, its about what is best for the child(ren).
So, for an example...
Child is in school
Mom works days and is home with the children in the evenings. So, the children will be with a parent when they are not in school...both mornings and evenings.
Dad works 2nd shift and goes to work before the child gets out of school, or immediately after and is not home until after the child is in bed. That means that on dad's days the only time the child sees a parent is in the mornings before school. It is not in the best interests of the children for them to be with a daycare provider when mom would be with them.
Change it up....Dad still doesn't work day shift, but works third shift...In that instance dad can still be with the children during their non-school awake time, they just need an overnight sitting while they are sleeping...that is not nearly as bad.
So really, its all about what is best for the children, not whether or not the parent has adequate access to child care.