I think it would take much less than a month+.

Assuming friendly territory, we have a distance of 1164 km by the path of modern roads. At walking pace, the average distance expected to cover in Europe was 30 km, so around 40 days.

Taking the speed of a horse into account, and the prevalence of roads in Germany and the Netherlands after crossing the apls, the horse rider should be able to make it with quick pace in 10 days.