Piwik doesn't use a rolling window. It may seem that way for Visits by local time, but this time is relative to the visitor.

I didn't understand why it was closed...

Attachment: Difference between two graphs for current day: local time visits and server time visits
Difference between server and local time visits.png

The image I attacched show the differences: server time visits by day hour fill the 24 hour enlarging the single bar width.

The effect is ugly.

What impides to have the server time visits plotted with the same parameters as the local time visits?

Attachment: Another graph pair with less hourly visits
Difference between server and local time visits - 2.png

The last attacchment shows that the problem isn't related to void hours.

I think I understand now. Your proposal would undo the change in #2316. You'll have to convince Matt...