Moodle cannot tell the difference between a genuine case of 'internet connection lost' and 'student unplugged disconnected their network, got out their mobile phone and started Googling'.
Therefore, the way Moodle time-limit works, is that it is the amount of time between when the student clicks Attempt quiz and Submit all and finish.
If your students are in a classroom setting, then you don't have to use Moodle to time the attempt. Just tell them when they can start and stop yourself.
