hitching to and from the fimmvörðuháls trail

Skogar bus runs all year, see straeto.is. Thorsmork bus stops mid Sept. If you are wanting to walk after that, it's probably too late. In fact it's probably too late already by mid Sept, take local advice. A normal 4wd can't drive to Thorsmork, so hitching probably isn't easy on that road.

I gave this same advice in more detail just a few days ago, search for it.

thank you, how long should the trail take to complete? can it be done in 7-8 hours?

can it be done in 7-8 hours?

It can, if you are superfit and encounter no terrible winds. Normal fit hiker reckon 10 hrs, potterer 12-14. I said this in a recent post, so you didn't look.

sorry friend I am very busy, I will look now ;)
and thanks for the info, I think I will take 2 days and spend a night in the hut

Buses stop service for a reason! You are off-season for that hike. On the other hand I know people who crossed Iceland from north to south in winter.

Walk it both directions and take bus to/from Skogar.