In Comic 41, Steve manages to build a time machine, which he uses to bring future versions of Beaver and himself back in time to tell them about the future. However, after Future Steve accidentally kills the father of the guy who brought about world peace, they realise time travel is too dangerous and go back. Or, well, forward.
Later, in Comic 112, Steve has finished the work on the machine and goes on a time trip back to Comic 42, against Beaver's warning. He takes his own cookie, enabling Cyber-Spook to succeed in throwing red paint on his past self.