Quickbase doesn't have a native option that I am aware of for seeing which users interacted with a table over a period of time. The easiest way to implement something like this would be to have an intermediate table between an "Assocaites" table and the "Projects" table and call it something like "Active Members". You could then have the project lead add or remove records to keep track of active members of the project.
Another option would be to create a multi-line text field with logging enabled. Then create a formula rich text field equal to "user()". Then create a form rule that says "whenever x happens, change the value in the text log field to the user field. Then problem would then be that you have a running list of users and time stamps that would take a decent script to slice apart and perform logic to remove duplicates and check date ranges. That formula would be beyond my abilities in QB unfortunately.
Maybe Dan Diebolt or someone can pitch in here.
