Depends on when you're going, daytime/nighttime, weekend/weekday. Plus I don't know what's the speed limit and the traffic on Czech highways.

Avoid daytime and weekdays, on a saturday, starting 8pm it is definitely possible to get to the czech border under 2 1/2 h, some crazy guys might do it under 1 1/2 h. But I presume you're not riding "Gumball" style.

Trucks aren't allowed on the Autobahn during the weekends, plus you don't have any buisiness travel ("Berufsverkehr") that makes it more relaxed to go on a Saturday or Sunday, if you need to go on a weekday only drive during the nights (after 8pm), otherwise you're going through hell, especially on the A3 and A6 (A8 would be even worse). I'll promise you that.