JFK-Arlington/Arlington-JFK

12:24 - arrived at JFK
12:31 - departed JFK
12:41 - arrived at Park
12:46 - departed Park
12:50 - arrived at Arlington

Total commute: 26 minutes
MBTA estimated total trip time: 21 minutes
discrepancy: +5 minutes
Total time in transit: 14 minutes
Total wait: 12 minutes

16:14 - arrived/departed Arlington
16:18 - arrived at Park
16:19 - departed Park
16:29 - arrived at JFK

Total commute: 15 minutes
MBTA estimated total trip time: 22 minutes
discrepancy: -7 minutes
Total time in transit: 14 minutes
Total wait: 1 minute