I put mine on the night before, right when I'm going to bed. Usually between midnight and 1 a.m. Just personal preference. It eliminates one task I have to do in the morning when I wake up.
The rub I use does not have a lot of salt in it, and is low on the salt scale as compared to other rubs. Last year, I forgot to rub my ribs before bed one time, and then rubbed first thing in the morning (usually 2-3 hours before going on the cooker). When I did so, I didn't notice any difference in the end flavor, and in fact placed 7th out of 63 in ribs that day. So I think you're fine either way, as long as you don't use a rub with a lot of salt.
Bottom line, test it and see what works best for you. You'll know if it gets "hammy". Then you'll need to reduce the time your ribs are in the rub from there.