When you enter an area, a stopwatch starts counting. Every five minutes of overworld time, (not in a battle, cutscenes, or a menu,) a check happens. There is about a ~15% chance at the first five minute check that a Time-Space Distortion appears. This chance increases at every five minute check, and by 25 minutes of overworld time, there is a 25% chance that a Time-Space Distortion will appear. Every time you enter a menu or battle, the stopwatch pauses. If you return to Jubilife or take a rest, the timer restarts.
So, the most efficient way to make a Time-Space Distortion to appear, is to just sit at Base Camp, and then check on your map if a Distortion is happening every five minutes. You can do this while mainly AFK.
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