I do not remember exactly, I think the cabins in 202 are 45 minutes. This may vary from one establishment to another, so you better ask at the reception desk. You can pay extra to stay longer, you can make the arrangement in advance or you can go over the clock and the reception desk will charge you for the additional time.
By the way, I have never paid 250 in a sauna. So the 150/200 that I pay grant me his full attention during the time in the cabin, I recommend you to discuss and agree on what you want to do before getting in the cabin. Additionally, you will get a lot of attention before going to the cabin (including making out and mutual touching), and depending on your generosity afterwards. I would add to the 150/200 one or two drinks to reward the attention pre and post programa.
If you want to make your 150/200 last longer, do not tell that you are visiting just for a few days. Make them believe that you will be there for months, and they will take care of a potencial regular generous client.