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.

Please give me some link to the "the day in Genesis is mistranslation" I'd like to read about it, since the only thing I can find is:

http://www.mechon-mamre.org/p/pt/pt0101.htm

"ח וַיִּקְרָא אֱלֹהִים לָרָקִיעַ, שָׁמָיִם; וַיְהִי-עֶרֶב וַיְהִי-בֹקֶר, יוֹם

שֵׁנִי. {פ}

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:

http://biblehub.com/hebrew/yom_3117.htm

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.