There is a lot of reading out there on the various types of instabilities, but generally the timescale for these effects are in the microsecond to millisecond range. I think particles move toroidally in the transsonic range, which depends on the temperature (which is a gradient from the core). This would be in the range of 300-1000 m/s in a device with a circumference of a meter or less (for most science machines made so far). I think it only takes a handful or orbits for an instability to grow. It depends on how much abnormal magnetic shear there is. I’m not comfortable saying more.

https://www.energy.gov/science/fes/articles/zero-tolerance-t...

http://www.ccfe.ac.uk/assets/Documents/POPVOL17p082509.pdf