I believe the XTools edit counter is skipping an hour (23:00–23:59 UTC) when displaying the time card.
Typically, it groups edits and displays their relative frequency in 2-hour UTC blocks: 02:00 (01:00–02:59), 04:00 (03:00–04:59), ..., 22:00 (21:00–22:59). I would thus expect that 00:00 displays 23:00–00:59, starting on the preceding day.
The 00:00 block seemingly does not include 23:00–23:59 UTC of the preceding day. This is evident because edit counts on XTools are consistently lower for this block despite other edit counters perfectly replicating the other 11 blocks and displaying what should be a high aggregate for the 12th, suggesting that something has been skipped.
Steps to reproduce
Examine my edit count:
- https://xtools.wmflabs.org/ec/en.wikipedia.org/ComplexRational (Xtools, apparently not working)
- http://project.paragram.org/wpuser/?lang=en&tz=0&query=ComplexRational and https://tools.wmflabs.org/dewkin/ComplexRational@enwiki (These are identical to each other and do not make that omission)
Also compare, with these three tools, the edit counts of other users who are consistently active between 21:00 and 03:00 UTC. The same inconsistency should persist.