How often does a timing belt need to be changed in a suzuki jimny?

About every 60,000 miles is what I remember (from when my son and I owned a total of 4 Samurai's about 10 years ago.) I certainly would not go over 100,000 miles without changing it. On the plus side, it's pretty easy to do if you are at all comfortable with a wrench, and the procedure is spelled out nicely in a Haynes manual. I found it easiest to remove the front grill and radiator, neither of which takes much time and effort, and it gives you a lot more room to handle the timing belt change. I don't think it is actually NECESSARY to pull the radiator and grill, but to me it made sense as it made the overall job easier. While at it, I would flush the cooling system, and replace the upper and lower radiator hoses, and the thermostat. Easy pro-active maintenance procedures, especially if you use your Jimny for off road driving where a breakdown could be more awkward to deal with.