Rolling Look-backs In Excel With Intermittent Zero Value Cells Throughout

I've got a spreadsheet that lists employee hours worked by week, I'm trying to create a function that would give an automatic look-back of both 90 days and 6 months. I've found some useful answers in other threads, but they tend to hinge on a zero value cell signaling the latest week (not) worked; however, for this purpose, some employees may have zero value fields for some weeks but have worked others.

I'm looking for a formula that can be uniformly applied to all employees in the spreadsheet and average their weekly hours for the past 90 or 180 days without having to update the formula each week new hours are entered.