I this morning know
Where we shall find him most conveniently.
In Scene ii. Horatio says of the ghost:
My lord, I think I saw him yesternight,
and Hamlet declares:
I'll watch to-night.
Upon the platform, 'twixt eleven and twelve
I'll visit you.
This watch and its events are given in Scenes iv. and v., while the third scene fills out the day, before the night comes on.