The use of the English word 'days' is effectively a mistranslation. As for the seventh day, that's a context switch for some life advice: after work must come rest, trying to work a seven-day week is stupid and harmful - something quite a few people nowadays would do well to remember.
And God called the firmament Heaven. And there was evening and there was morning, a second day." (Genesis 1:8)
Which word of those is mistranslated?
Note that because of this and similar lines the Jews count the days for celebration (including Shabbat) to have a beginning at the evening (Shabbat starts on Friday evening).
If you mean "yō·wm" here are all the places where the word was used in the Bible:
It's the almighty that had to rest, not the people. The absurdity is obvious for everybody except the believers. But that is the definition of faith, believe, no matter what.
