Worked until midnight for weeks on end?

[Englishfan]

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.

[Mister Micawber]

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Not no end-- on end. Weeks on end means week after week (envision all the weeks in a row, end to end to end, etc.)
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Native English teacher at Mister Micawber's