"After six hours at the airport, František stopped waiting."
Translation:František po šesti hodinách na letišti přestal čekat.
František přestal čekat na letišti po šesti hodinách. Mělo by být uznáno.
Taking into consideration that word order in English is more rigorous, the emphasis in an English sentence (like this one) is about intonation. Maybe the compromise is to add the grammatical Czech versions as well. It will be also better for understanding how the Czech word order works. Also comparing every version of a Czech sentence to the English one is very time-consuming (I guess). It is just how I see it.
I thought that after any numbers above four you have to use genitive, so why inflected "hodinách" here