Using the Tether app version 4.6.14 (current latest version in Google Play Store) on Android (Samsung S21), my router (curent latest firmware) shows traffic statistics in the future.

Day view screenshot at 12:00 AM on Tue July 16 shows some data use at the end of the day. It should be at the start:

Week view screenshot at 12:01 AM on Tue July 16 shows a huge amount of data use for Tuesday, which is completely wrong after only 1 minute of the day:

Week view screenshot at 7:52 AM on Tue July 16 shows a huge amount of data use for Tuesday, plus some data use on Thursday July 18 - which is 2 days in the future:

The data use shown for Thursday looks like my data use for this morning (Tue July 16), because it has been increasing during the morning.

It seems likely that this problem is related to my time zone, which is UTC+9:30 Adelaide. It is rare to have a time zone with a 30 minute offset, and it may not have been tested.

Hopefully it's an easy fix.