It is very hard to know exactly how you should sauna bathe as every body is different. In short, each body will react to the heat stress differently.
We recommend finding the lowest temperature where you have a good consistent river-sweat, and you want to stay in for at least 10 minutes. Every few days/weekly you can increase the temperature by 10 degrees and the time by 10 minutes. The higher temps and longer times will have the most beneficial results.