@gcodori
Unbelievable as it may be, it's exactly how Mujaki worked - it was understood implicitly that Shouta's older body was still alive (remember how Rio did CPR on him) even during his time travel. He found out that the URAN version of time travel uses multiple time-line theory - changes won't change existence, but they can potentially affect lifestyle and whatnot (ex: Shouta getting Rio in one line thanks to saving her from a truck)
In this case, though, our chunnboyu girl Suzune (also from Mujaki) was with Shouta during a time jump, and realized even back in Mujaki the specific necessities needed to do proper time jumps. This was to the point that both she and Shouta was even able calculate the exact time needed to jump back to Shouta's old life, despite it being so dreary - all so that he can save Konomi.
From that time, Suzune became a uni prof, and for some reason, taught our little girl how to time jump. For what reason? God knows.