Hello @Klaus-r,
as I was using MRA in parallell with my Garmin XT2 and experienced that the difference between MRA and the Garmin device even on routes with more than 300km is in a range of 5-10 Minutes. This difference is coming von minor differences within the final routes.
My understanding is, that MRA and Garmin are using the same routing algorithm. Seeing this minor differences between MRA and Garmin this seams to be correct.
I know that Garmin had something like the individual speed definitions for specific road types, but this is no longer available.
Personally I don‘t see really relevant differences between the planned times and my reality on my routes. I don‘t think, that a difference of a couple of minutes in a tour is no problem for me.
Greetings
Thomas