Probably not as common a phrase, but is "It could have been ten hours" OK? Like if you were talking about how long something was going to go on.
The Czech sentence is specifically about the time of some event in the past and not about duration.
If it were "Mohlo to být (tak) deset hodin.", it could be an answer to a question sbput durstion of something.
I am not really sure if you are asking about the Czech or the English sentence. The translation is quite straightforward.
You mean when guessing the current time? "Může být deset hodin." Often we will add "tak" or "asi" or "přibližně" before the time in this case.
I’ve been having some difficulty with this myself. There are no Tips & Notes yet as far as I can tell, so we’re having to use a bit of guesswork. If I understand “mohl” and its variants correctly, they signify the past tense. If so, then part of the challenge in the translation is that, in English, you can / could use both can and could (or might, or whatever) to describe a current event (i.e., “We can go now, if you like...” - present; “It could be ten o’clock now” - conditional present). I’m reminded of the difference between “ich könnte” and “ich konnte” in German, both meaning “I could” (e.g. “I could destroy a hamburger right now” versus “I could run like the wind back in my prime”, or whatever).
If Ithats what’s going on, then, “mohl” might be used for the past-tense version of “could”, but correct me if I’m wrong.
(Note: edited for clarity shortly after posting.)