Learn Russian: Я ценю пунктуальность, ведь поезд отходит в двадцать минут пятого. - I appreciate punctuality, after all the train leaves at twenty minutes past four.

In Russian, to express the time for the first half of the hour, you refer to the hour that is currently underway. Since the time is past four o'clock, you are already into the "fifth hour". So, двадцать минут пятого literally means "twenty minutes of the fifth (hour)". Пятого is the ordinal number "fifth" in the genitive case.

Why is the preposition в followed by двадцать here?

To say "at" a specific time involving minutes, Russian uses the preposition в followed by the accusative case. The number двадцать looks exactly the same in the accusative case as it does in the nominative.

How does the word ведь work in this sentence?

Ведь is a very common emphatic particle and conjunction. Here, it connects the two ideas and is best translated as "after all" or "since". It is used to justify the first statement by pointing out a known or obvious fact: I appreciate punctuality because, as we know, the train leaves at exactly 4:20.

Why use отходит for the train leaving instead of a verb of motion like уезжает?

While уезжает means "drives away" or "departs" and is perfectly understood, отходить (literally "to step away" or "move away") is the standard, idiomatic verb used for the departure of scheduled transport like trains, buses, and ships.