That is correct. Both forms are correct, but můžu and můžou is far more common in spoken Czech.
Also notice that unlike English or French there are almost two different languages (OK, just dialects) existing in most of the Czech Republic. The standard (literally Czech) and Common Czech.
There is almost no-one who would be a native speaker of standard Czech, we are either native speakers of Common Czech or some other dialect. We learn standard Czech from reading books (or from listening to fairy tales being read to us), from watching fairy tales in TV and in kindergarten or school.
All Czech-as-foreign-language courses teach standard Czech and a lot of what you hear in the streets would be different and often plain unacceptable for such courses. The last skill of this course is about Common Czech.
lxbrat The point here is that it is the native dialect of the majority of the population and still it differs so much from the sandard. It is really not that common. Of course there are also other dialects in Czechia, but that is common everywhere.
Silesian is not a good example. It is a geographically limited region and mixes Czech and Polish.
And a dialect is certainly NOT when people do not understand each other. Such distant dialect are usually considered separate languages. And yes, that's why Silesian may well be regarded a separate language, not just a dialect https://en.wikipedia.org/wiki/Silesian_language
You could use "another four hours" as shown, or "four more hours," which is also accepted. "I cannot wait for next four hours" is incorrect in English. (Native AmE)
UPDATE (4 Jan 19)-- Reading this again, I would say that "I cannot wait for THE next four hours" would be fine in English, in the right context. But it would be best for one of the CZ natives on the team to decide whether it should be added as an acceptable translation.