The train at 6 in the morning indeed takes 4:02, while the other two later in the day take 3:58. The "less than 4 hours" used in their marketing really means just slightly less.

@HenningMakholm Guess the data is historical: en.wikipedia.org/wiki/Rail_transport_in_Iceland

What exactly are you asking for?

@ventsyv Do they usually claim valid infractions, so that you can prevent this by driving lawfully? Or do they make something up and just back each other?

Any time on the day of departure or arrival should be fine, as a flex ticket allows you to use other trains (and not just the one for which you have a reservation) as well. I don't know of any time limitation, though I've never stayed more than 90 minutes. However, note that they are usually only open from 7:00 to 21:00 on weekdays and 8:00 to 20:00 on weekends.

Actually, the 1st class section of the DB Lounges (available in Berlin, Munich, Cologne and Frankfurt) does serve alcohol. I've had a couple of beers for free there, not sure if they have wine as well.

Perhaps more importantly, stay away from gas stations on the Autobahn. They're far more expensive at any time. The so-called Autohof (which are close but not directly on the Autobahn) are a bit cheaper, but still more expensive than a standard gas station.

The master card locator shows one at "OVARIEVEGUR 5, SØRVÁGUR, VÁGAR". The location on the map for this one is very likely wrong: on a steep mountain slope in the middle of nowhere. But address suggests it's located in the town I was looking for. It's not listed on the openstreetmap data, though, so either this is incomplete or the atm is a ghost.