Finding the average number of days (or weeks) from a column

Guys,

I am trying real hard to figure this out myself but unable.

I have a column (column AR) in a table with 9642 rows. Not every row has a duration (as seen in screen shot), some are blank or nul. The footer totals the column hence the duration of 4508 weeks. Column AR is the time a vehicle was "on lot" (car lot, auction, wrecker services, etc)

What I am needing to do is get the average time of the rows with data in column AR. So I have a search by start date and end date. If that search shows 100 rows, for example, but only 70 (random number for this question) of them has time "on lot" totaled in that row: I would like to know the average of those 70 rows.

I have all the other formulas and calculations working except the average time on lot. So, I have start date of 01/01/2022 and end date 08/31/2022. I would like to know the average of the total of 4508 weeks as shown below. (these are actual search dates which shows actual total of 4508 weeks). Screen shots are just for visual - remember there are 9642 rows and growing.

I also narrowed the search down to 01/01/22 to 01/10/2022 which changed the time on lot to 20 weeks. So something is working but not calculating the output I want.

For reference to the calculation screen shot: "All Assignment Data::AI" through "AW" is referencing a true/false statement to gather my sums. The final calculation is placed in a different table from the one screen shot but please feel free to put in the 2nd footer row (I can move it on my end). Again, images are just for reference. The search dates will determine how many rows there are.

First image is a screen shot of a reduced view of the master table. Second is the target cell in another table that currently has the calculation that I last tried.

Thank you