"No left turn (except school busses) 7-10" or, rephrased "from 7-10 no left turns, except school busses", is my vote, versus
"No left turn (except school busses 7-10)."
Why would they ban it 24/7?
There's a town here that bans right turns onto a 2-way street. If done successfully, it would let the traveller cut through a rich neighborhood and miss a congested light. There's a millimeter of road length you're not allowed to travel on in one direction!