You can set a maximum time, use a timng/ hourglass widget. But a minimum time? Maybe hide an Exit button but closing a window is alwasy possible. Seem bit of a silly requirement IMO.
The state of California is filled with silly legal reqirements. Still, there are other courses with minimum time reqs (i.e., online traffic schools).
Are you using SCORM?
If so you'll more than likely need to add some functionality into the scormdriver.js to stop the course from writing completion if the cmi.session_time does not equal at least 120 mins.
Yes, SCORM, AICC and hopefully Tin Can in the future.