שֵׁ֣שֶׁת יָמִים֮ תֵּעָשֶׂ֣ה מְלָאכָה֒ וּבַיּ֣וֹם הַשְּׁבִיעִ֗י יִהְיֶ֨ה לָכֶ֥ם קֹ֛דֶשׁ שַׁבַּ֥ת שַׁבָּת֖וֹן לַיהוָ֑ה כָּל־הָעֹשֶׂ֥ה ב֛וֹ מְלָאכָ֖ה יוּמָֽת׃
Six days shall work be done, but on the seventh day there shall be to you a holy day, a sabbath of solemn rest to the LORD; whosoever doeth any work therein shall be put to death.
Rashi on Exodus
ששת ימים SIX DAYS [MAY WORK BE DONE] — He intentionally mentioned to them the prohibition in reference to the Sabbath before the command about the building of the Tabernacle in order to intimate that it does not set aside (supersede) the Sabbath (cf. Mekhilta d'Rabbi Yishmael 35:1:1).
Sforno on Exodus
וביום השביעי יהיה לכם קדש, and you may not violate the Sabbath even in order to complete the Tabernacle sooner, although the work on the Tabernacle is also a sacred task.
Or HaChaim on Exodus
ששת ימים תעשה מלאכה, "during six days work shall be performed, etc." The reason the Torah emphasises the work to be performed on the weekdays may simply be a hint that if one observes the seventh day as a holy day, the work required for our maintaining ourselves during the subsequent six days will take care of itself.