This weekend we made two longer trips in the daytime in NL. The ETA's our GO 5100 gave were off quite a bit. Both times about 15 mins. This seems to be a problem when driving in the daytime when there's a blanket speed limit of 100 km/h in NL and the route planned is mainly on motorways that used to have a 120 or 130 km/h speed limit. Our GO 5100 does know all the speed limits.
It's very irritating to see the ETA creep up by a minute at the time during the journey and you arrive about 15 mins later than originally predicted.
Interestingly when you plan a trip on the My Drive Connect website you get a clear difference between day and night of about 15 mins for the trips we made this weekend.