Just to clarify, he's not in a Time Chamber of sorts.
What happened to him is the same shit Mayuri did to Szayel in Bleach, Kurama did to Older Toguro in YYH and Itachi did to Kabuto in Naruto.
He's stuck in a time loop, or in an altered time scale, but ONLY inside his head.
I wonder why we keep waiting for an awesome battle when in reality this encounter is going to be simple.
I mean, unlike the twins BF, Junko's BF really loves her and they do plan to spend their lives together.