Translation:We practiced for two months.
We should also accept "style" because we are learning Chinese, not English. Remember? :-)
By the way "practice" is a noub and "practise" is a verb. If you don't care for the difference, you might as well say "We footballed for two months" (assuming you were practising playing football)..
I am American, but i favor "practise" because it is more fonetic. I am a firm supporter of (ov) English spelling reform; "foneticizing" as i call it; given that millions of English-speakers ar functionally illiterate, no-one (-wun) should be able to, in good conscience, choose the clearly-less-fonetic ov two or more accepted spellings.
Actually, Chinese doesn't have tense as a grammatical category, but it does have aspect (perfect and imperfect)--so in fact both sentences can be translated as "have practiced" (perfect/completed aspect). It is true that present perfect tends to describe events that have occurred, and hence these can be framed as past tense (i.e. in languages that have tense).
The second sentence, where there is a sentence-final 了, can be interpreted as conveying other information, such as change-of-state.