It seems 30 seconds is the magic number. After you remove the iron, wait 2 minutes. If it didn't work right, don't worry. Clean the board with acetone and start over. Etch the board with ferric chloride or whatever you use.
Many people prefer ammonium persulfate.
Before you remove the toner resist, drill holes in the board. The little holes in the copper will help you drill and the toner helps you see them. After you drill your holes, use acetone to remove the toner. They tell me that the copper will eventually turn green if you don't do something. This trace consistently doesn't come out right.