Mary Cooch

No -that is irrelevant. Please post exactly in what way it doesn't work, with screenshots if needs be.

In short, yes. You can have as many users on your Moodle as you want. There is a longer answer however, and that depends on who is hosting your Moodle. If it is in house then there is no limit, but if you are paying a company to host your Moodle then they might have put limits on the number of users you are allowed - storage size, bandwidth, all those other things... Some companies have a sliding scale for selling Moodle according to how many people use it. (And nobody needs a license, btw)

Here are the instructions for setting up Mnet, assuming of course you have an installation of Mahara ready to go http://docs.moodle.org/en/MNet You need to first enable Networking in Administration> Site administration > Advanced Features. 

Can you post a screenshot of the assignment settings relating to times?

Yes. Please see 2.1 here "Restricting access to course sections" http://docs.moodle.org/en/Conditional_activities_settings