No, the learning commons is not 24/7.
And OP, you might have seen some parts closed off because not all sections open at the same time. However, the main library (including computers) open at 8am, as does the service desk, so there should be someone around to ask if you're having trouble.
Hours for each section on each day can be found here: http://library.mcmaster.ca/hours-info/week/2014-W38
(or by a quick google search).
If you're THAT paranoid you can go to a community library tonight to print it.