Worked until midnight for weeks on end?

Hello my dear friends, it’s me again who needs your help. I’m just reading this article and there some things I don’t seem to be getting. The first phrase is in this sentence:
We worked until midnight for weeks on end.

Now, what does no end mean here? I understand you can work for weeks without a weekend but but how you can work no end?

I’ll post my other questions in separate messages. Thanks in advance.

Not no endon end. Weeks on end means week after week (envision all the weeks in a row, end to end to end, etc.)