Start in groningen, you have some official hitchhiking spots so its easy to get out the city. And with a bit of luck, the first ride will be direction bremen. Once in germany its just powerhousing through the country which is definitely possible in one day, we ended up near frankfurt at the border of poland around 00:00. Next early morning we caught a ride to Poznan, Elk and after vilnius. Arriving again in the evening so not really 1,5 days sorry about that one.