How to calibrate the time constraint of an exam for a new course?
This is totally unscientific, but for my exams (mathematics) I use the following rule of thumb:

After writing the exam, I sit down with a stopwatch and work the exam from start to finish. Of course, I know how to solve the problems (since I wrote them) but I go carefully through all the steps and write what I would consider a thorough and exemplary solution. I note the time I spent  on each problem.

Then I take the total time and multiply it by 3 (or sometimes 4). If this exceeds the allotted time for the exam, I remove or simplify some questions. (This is where it helps that I wrote down the time I spent on each question, so I can remove a question and recompute the time without actually retaking the whole exam.)

As a side benefit, this also helps ensure that I haven't made any mistakes in creating the exam, and that all the problems have the solutions I intended. It also gives me an answer key.