Been having some difficulty trying to match up the traffic graph display with known usage patterns so I did a check yesterday by initiating a large download so it stuck out from the background. It initially showed as the correct period (1300-1320) in the traffic graph. Over time the displayed period slowly shifted until it now displays as 1700-1720, suggesting the actual traffic plot covers approximately 28 hours rather than the 24 hours of the axis legend.

Anybody noticed anything similar with other routers/firmware versions, or is it particular to this combination?

I think you may be right, the timescale on my 2927 traffic graph looks decidely suspect! Comparing the daily traffic graph [Diagnostics >> Traffic Graph] from my 2927 against PRTG which I use to monitor WAN throughput shows exactly the same traffic pattern but with the timing skewed in the Draytek graph. For example checking on the last 24 hours [snapshot taken at 09:54] shows a PRTG peak at approx 21:00 whereas the 2927 daily graph shows the same peak at (approx) 22:45


 

Glad it's not just me!

I dug out an old 2860, kept as an emergency spare, and looked at the traffic graph on that and the time axis runs for the previous 30 hours in day mode, which would probably align with what the actual plot in the 2927 is scaled to. Looks like the scale on the time axis is incorrectly drawn on this model.