For example, in my grammar textbook, the sentence:
昨日は3時から5時まで友達とテニスをした
Is translated as "Yesterday, I played tennis with my friend from 3 till 5." Which implies that the speaker was playing from 3 up to, but not beyond 5 (so for 2 hours).
In the notes section however, it says that まで includes the time that it is preceded by:
来週の月曜日まで休みます
means "I will be absent until next Tuesday", i.e., in this case まで includes Monday (月曜日).
Which is correct?