Specific day for 5 domains/week limit lift?

Certificates/Domain you could run into through repeated re-issuance. This limit measures certificates issued for a given combination of Public Suffix + Domain (a "registered domain"). This is limited to 5 certificates per domain per week.

Is there a specific day and time in the week for the 5 certs/week limit to lift?

This means in if the first of five zertificate was issued longer than 168 hours you can issue the next.
It is not per day but per timeframe. i think

My understanding is that it’s within the past 7 days, or 168 hours as tlussnig wrote. Basically, it’s a floating window. Assuming that understanding is correct, the language should probably be modified to make that clearer.