Time Expression in Russian

One tricky thing for foreigners is the translation of “for” in the expression of time. If I say:  

• “Я жила в Москве 5 лет.” (I lived in Moscow for 5 years.)

• “Я приехал в Москву на год.” (I came to Moscow for a year),

Note that in the first sentence, we don't need any preposition, while in the second sentence the preposition “на” is used.   How comes? When you want to express the time, during which something is happening or has happened then you don't need any prepositions.  

• Он работал в этой фирме 15 лет. (He worked in this company for 15 years.)

• Антон ждал её полчаса. (Anton waited for her for half an hour.)

  When you want to express the approximative time needed to do something, then you need to use the preposition “на”:  

• Без пробки, вы можете доехать сюда на час. (Without traffic jam, you can be here in an hour.)

• Зайдите ко мне на минутку. (Come to my place for a minute.)

  The expression of time can also be express with the preposition “за”. But it will be translated in English by “in, within”:  

• Он не успел прочитать эту книгу за неделю. (He couldn't manage to read this book in a week.)

• Брат изучает русский язык 2 года. Он думает, что русский язык можно изучить за 5 лет. (My brother has been learning Russian for two years. He thinks that Russian can be learned in five years.)

• Я собираюсь закончить эту работу за 5 часов. (I can finish this job in 5 hours.)

In that case, we need to use the perfective form of verbs.