[Arroway]

In the act 1 Geralt said Iorweth that it's two days travel on foot to Vergen from Flotsam, and then in the beginning of act 2 we can see a title - "two days after living Flotsam". But they floated there on the prison barge or on Roche's ship if it's Roche's path.
So how do you think is it mistake in Geralt's words or what?
Sorry for my english

[Guy N'wah]

If Iorveth had to march his army to Flotsam, it would be a two days' march. This is before Geralt knows of the plan to hijack the prison barge. No mistake.

And it wouldn't be much faster by river barge than it would be on foot.

[Arroway]

So is it clearly means they floated to Vergen/Henselt's camp exactly two days without any delay and landed there in the same time of Saskia and Henselt meeting?

[Guy N'wah]

It does show in game that they arrived at the same time as the parlay between Saskia, Stennis, and Henselt. Since this was not an event scheduled in advance and communicated to the parties in Flotsam, it implies only that if Iorveth and Geralt had been slower, they would have missed all the fun.

[Arroway]

I mean, I just look at world map, on path they did on ship and can't believe that it's possible to pass distance from Flotsam to Vergen in two days on foot as Geralt said...

[Guy N'wah]

We have no information as to the scale of the map. Elves travel light and would be very fast on foot. River boats are not fast to begin with, and that nasty old barge would be especially slow. I don't see a problem, other than possibly trying to make too much of the timeline.

[WrathAscending]

They're also travelling up-river, with the current against them all the way and probably a need to avoid detection since the ship is crewed by condemned war criminals and carrying the man believed to have killed Foltest. That said, "two days by foot" may have been the pace Geralt could keep up by himself, with limited breaks due to his superhuman physique and being able to keep travelling through the night thanks to his mutations. The Scoia'tael may well not have been able to keep up.

Two days on foot might also have resulted in a midnight arrival, but travel via the river gave a morning to mid-day arrival.

[Sirnaq]

It's funny that every single horse in this game magically disappeared.

[WrathAscending]

Well, as we know from the books they can only be controlled using the Axii sign, so...

That said, a sufficiently fit human (and Geralt definitely qualifies) can outpace a horse over the period of a day. You can;t ride them too hard for too long, unless you really don't care about their health.