Between Act I and Act II eight days pass. We know this because at the beginning of the act the stage directions read that the setting is in "Proctor’s house, eight days later."
We do not know exactly how much time passes between Acts 2 and 3, but we are lead to believe it is a continuous passage of time (especially since no time marking is denoted.) At the end of Act 2, Proctor tells Mary Warren that the two of them are going to the court to clear Elizabeth's name
You will tell the court what you know....My wife will never die for me. I will bring your guts into your mouth, but that goodness will not die for me.
Since the men (Giles Corey, Francis Nurse, and John Proctor) have enough time to get a deposition together and signed by 91 people of the town, we are left to believe some time has passed.
Between Acts 3 and 4, three months pass. Again, the stage directions tell us this by stating "three months later." This is the longest break and time, and possibly the most important. During these three months, the town has fallen apart. As Cheever tells Danforth "there be so many cows wanderin' the highroad" and the crops are dying on the vine. Instead of having people to take care of the cows and crops, they have all been jailed or executed.