Find the duration in weeks between grouped events using the 1st of each event

I have a data set where i'd like to have the duration between each grouping of events by comparing only the first (earliest) event in the grouping as a google sheet arrayformula. The output should be in weeks. Please see the picture.

Assumptions that are made here are:

1. Dates will be going in ascending order as shown
2. There will be no skipping of dates
3. A grouping will always have consecutive checked boxes. Meaning, there will never be a case where day 1 will be checked, day 2 will not, day 3 will be. AND all that considered one group. So if there's an unchecked box it means a new grouping will be started whenever there's a new checked box.

Thank you in advance!https://docs.google.com/spreadsheets/d/1E1Gg6aJmagctMwSYIK7RPmwYiFqGMCDMDFu1CTIx5yM/edit?usp=sharing