Temp depends on culture acidification rate. If you ask your supplier for the manufacturing spec, they will give you a chart that has acidification curves... usually 3-5 at various temps, from about 85 to 105 for meso, and 90 to 115-20 for thermo cultures. We might have them in the library here as well. You can use those curves to target the rate of acidification so that you hit your time targets and your pH targets, and that they correspond to the ideal make process you have designed after taste testing of the final product. That's the commercial approach, anyway, when striving for a consistent product.
The short answer is that the fastest acidification for meso bacteria happens at 103-104F, and 115-20F for thermo. If you leave them at room temp, the curds will eventually acidify, so the tradeoff is time to completion.