It is hard to get your head around especially when it is all new! He can't go too low if he is not on insulin. A normal cats ranges from 40-120 off insulin. We generally tell new diabetics not to shoot under 200.
He could climb some, but it is a real good sign he went down overnight. We just have to watch and see how he does. If he goes to 200 or below, I would just keep feeding the wet food and testing. If he would stay in the high 200s all day, we could possibly give him a mini dose - a drop of insulin - tonight.
It's up to him! We are just observing.