Being two different cultures, we expect some differences in telling the time. Occasionally, those differences can lead to confusion either from literal translation or improper notation.
In most official circumstances, people in the Czech Republic use the twenty-four hour clock. In more informal situations, they'll use the twelve hour clock, so even if you're not familiar with the twenty-four hour clock, subtracting twelve from the evening times shouldn't be too daunting and you shouldn't have any problem.
Noon or Midnight
The one occasion when there is confusion can be midnight and noon. Even if neither is technically a.m. or p.m., common convention has midnight as the former and noon as the latter. However, among colleagues and even with some businesses these can be mixed up. Therefore, if you see that an office closes at noon - and it's not a government office - you might want to check that they don't mean midnight.
Hours and O'clock
Sometimes the word hours and o'clock are confused. This is usually not a problem except in this one example I overheard recently between a Czech woman and her German friend.
Guy: What time does the festival finish?
Woman: In two hours.
Guy: It's so short?
After a moment the woman had realized her mistake, which anyone familiar with Czech would know was a literal translation of ve dvě hodiny, meaning 02:00, or 2:00 a.m. It might also be interesting to note that the word hodiny also means clock or watch. So if a certain time seems strange, it could be this reason.
Half and Quarter
The fractions of the hour are referred to differently than English, which can cause some confusion when going from one language to the other. Take for example 7:30 a.m. In English, that's half-past seven or half seven (British English). In Czech it is půl osmé, i.e., half of the eighth hour. As with the earlier example the word for hour, hodina, is usually dropped.
This difference can create confusion if someone says half eight. You might miss a meeting, or worse, a plane. This mistake is generally more common among older people. But if the time is important and you're not sure, it doesn't hurt to ask.
With quarter past and quarter to, the expression is also always to the number ahead, except the counting (cardinal) number is used instead of the ordinal number. What do I mean? The time 8:15 a.m. will be čtvrt na devět (literally a quarter to nine) and 8:45 a.m. is tři čtvrtě na devět (three quarters to nine).
Usually when time is expressed this way the twelve hour clock is used. The twenty four hour is used when the whole number is said, so 21:30 would be půl desaté or dvacet jedna třicet.
This is more confusion over a word than time, per se. The English word 'while' is often translated as chvíle. However, the sense is that chvíle is shorter than a while. So if someone tells you “It will take a while.” It might not be as long as you think. Unless it's the Department of Asylum and Migration policy, which might be longer.