However, you could use some creative options depending on the context:
* A week of days - This is the most common and straightforward option.
* A cycle of days - This emphasizes the repetition and natural order of days.
* A string of days - This suggests a continuous sequence of days, perhaps highlighting their duration.
* A span of days - This emphasizes the length of time covered by the days.
Ultimately, the best collective noun will depend on the specific meaning you want to convey.