Something like:
```python
for report in reports:
    try:
        next_report = report.get_next_by_report_date(user=user)
    except NGReport.DoesNotExists:
        longest_end = report.report_date
        break
             
    if next_report.report_date - report.report_date >= timedelta(days=7):
        longest_start = next_report.report_date
    longest_end = next_report.report_date
```
where reports is a query for all the reports of a user, should work fine. Just a suggestion, feel free to ignore it.