You can make golden doorways back in time for around a few minutes. it takes concentration to open them and maintain them so you can only open them nearby or through a screen, It gets harder and harder to chain multiple portals so you can't travel through days and days on end, Anyone passing through will replace their past selves but now have their future's injuries and possessions.
You can make a "time bomb" by looping light between 2 portals aided with your power to become increasingly more powerful with time.
(You're unable to go before your entry unless you have Homecoming)