I just generated a new MIT licensed repository on Github. Part of the license looks like this:
Copyright (c) 2017 superfly-css
What is the purpose of having a year in the copyright line? Is it just an indicator of when the copyright started?
Yes, it indicates when the copyright started and, therefore, when the material can be expected to eventually enter the public domain. Notice that some sites update the copyright year on existing content from time to time; updates years are invalid and do not change the real copyright year of the original material. As far as I can tell, it's not illegal to misrepresent the copyright date, but the true date is what has legal weight.