You can use 'Override Timedelta', but be aware of what it does.
TimeDelta is the time between two frames at runtime, and is measured very accurately. This is used to move objects so they move at the same speed no matter what the framerate is. The problem is if the framerate drops a lot, TimeDelta (the time between frames) becomes large, and Physics can be unstable when TimeDelta is large, because objects are often jumping large distances instead of moving smoothly, so objects can end up inside each other etc.
Overriding TimeDelta makes it always return the same value, so even at low framerates, objects are basically moving the same distance every frame. This means the entire game slows down if the framerate drops. It also means if you're V-Synced (and you should be) then your game runs twice as fast on a 120Hz monitor as opposed to a 60Hz monitor. If you're happy to accept this, then overriding timedelta is a good way to keep your physics stable.