is the map and guide book incorrect

Here's what some do to get accurate driving times:

input the route into viamichelin.com, as you've done.

cross-checking viamichelin by inputting the same route into googlemap.com

taking those two times given, averaging them if different,

and then multiplying the time by about 1.25, that is, adding about 25% more.

Taking the result of that and realizing that those times, from both sites, contain no allowance for stops of any kind, not even for the usual gas or comfort stops that have to be made.

Adding an estimate of the time for stops.

The result of the above starts to give you an idea of the time it would take.

Obviously all the times in viamichelin and googlemap assume "normal" road conditions, no rush hour through cities and no road construction.

The road from Prague to Dresden is 2 lane and can be slow. Trip also involves a border crossing from a non-EU country into an EU country. That will go much faster if your passport is stamped by immigration when you arrive in Europe. Otherwise, you'll need your boarding passes to prove where and when you arrived - expect a long wait while the guards check.

There is no border check between Prague and Dresden. Both Czech Republic and Germany are EU countries and also both are in Schengen zone.

There was still a border check when I crossed in summer 2007, but perhaps that has since changed.