I would always wipe it off before it dries. You'll have much better luck that way.
An even better system is to sand or sandblast the panel to metal, clean it with PRE and just shoot epoxy primer. That allows you to skip the acid etch step. You can then do body work on top of the epoxy and it won't rust. I even would spray panels that I knew I would be doing dolly/hammer work, cutting, etc. It was just easier to sand and respray over the worked areas than to deal with a completely rusted panel.
