You appear to have this relationship:
Members::__pkMemberID = Tracking::_fkMemberID
If so, then the following calculation: Tracking::DateOfVisit - Members::DateRegistered will compute the number of days between their registration date the first date logged in Tracking. (This assumes an unsorted relationship between members and tracking)
So you could set up a calculation field in Members with this calcualtion and then perform a find with > 30 specified as find criteria in this field to find all people who have not yet logged a first visit or that have a first visit that was 30 or more days after their registration date. Additional criteria can be used to filter out members with registration dates less than 30 days old so that this does find recently added members.
I think I understand what you're saying, but for some reason, when I put that calculation field into my members database, it's turning up blank. Is there a chance that my relationship is messed up? I have Members::Full Name=TimeTracker::Full Name as my only relationship between the layouts. thank you for trying to help me!
That relationship should not result in a blank field. Did you use a field of type calculation or a number field with an auto-entered calculation. If you used an auto-entered calculation, change the field type to calcualtion.
I do not, however, recommend that you match records by the full name field. Names are not unique, people change their names and names are vulnerable to data entry errors. Matching records by an ID field (auto-entered serial number) is much safer and avoids these issues with member names for the most part.