In Act III, Scene 1, the only reference to time of day is that the day is "hot," suggesting it is the middle of the day. The heat of the sun is riling the tempers of the young men.  Then in Act III, Scene 2, we hear Juliet wishing that night would come faster:

Gallop apace, you fiery-footed steeds, Toward Phoebus' lodging. Such a wagoner As Phaeton would whip you to the west And bring in cloudy night immediately.

She wants the day to go by faster (saying "Come, civil night") so that she can be with Romeo, to whom she has been secretly married. The nurse agrees to help Romeo climb cords up to Juliet's chamber and ends the scene telling Juliet to go to bed (suggesting it is toward evening). 

Hie to your chamber. I’ll find Romeo To comfort you. I wot well where he is. Hark ye, your Romeo will be here at night. I’ll to him. He is hid at Lawrence' cell.

In Act 3, Scene 3 Romeo and the Friar discuss Romeo's banishment.  We know it is not nightfall yet, as Romeo must be gone by that time.  The Friar warns Romeo:

Go hence. Good night. And here stands all your state: Either be gone before the watch be set, Or by the break of day disguised from hence.

This is another reference to the time of day.  Romeo can stay overnight but must leave before "the watch be set" or before daylight comes.The next scene (Act 3, Scene 4) between the Capulets.  We learn very specifically that it is Monday evening.

But it is Act 3, Scene 5, the scene between the two lovers in Juliet's chamber, that includes the most pertinent references to the time of day.  Metaphorically, Juliet says she hears the nightingale, the bird of night; Romeo does not need to go yet:

Wilt thou be gone? It is not yet near day. It was the nightingale, and not the lark, That pierced the fearful hollow of thine ear.

Romeo gently tells her it is the lark, the harbinger of day, and that he must go:

It was the lark, the herald of the morn, No nightingale. Look, love, what envious streaks Do lace the severing clouds in yonder east. Night’s candles are burnt out, and jocund day Stands tiptoe on the misty mountain tops. I must be gone and live, or stay and die.

Then, because he loves her he says that he'll pretend with her that the bird is the nightingale and let death take him: "I’ll say yon grey is not the morning’s eye." But Juliet then accepts that it is the lark and tells Romeo to go:

It is, it is. Hie hence! Be gone, away! It is the lark that sings so out of tune, Straining harsh discords and unpleasing sharps.

The lark is unpleasant to her because it means she must be separated from Romeo now that it is morning.  Then the nurse enters, saying "the day is broke" (it is morning) and that Lady Capulet is on her way.  Juliet again references the sorrow of morning:

Then, window, let day in and let life out.

After more words of farewell, Romeo leaves and Lady Capulet enters, asking if Juliet is up (another reference to how early it is).  Juliet seems surprised at her mother's early appearance, saying,

Is she not down so late or up so early?

We know from these lines that it is now early Tuesday morning, and Juliet is expected to marry Paris on Thursday.  She has just spent the night with her secret husband so it is understandable that she reacts with such horror to her parents' decree.