Is there day and night in heaven?

Yes. However, there won't be the sun or the moon we are used to, because it states in Revelation that they won't be needed. This doesn't mean that there isn't day or night, though. Here's why.

For this reason they are [now] before the [very]throne of God and serve Him DAY and NIGHT in His sanctuary (temple); and He Who is sitting upon the throne will protect and spread His tabernacle over and shelter them with His presence. (Revelation 7:15)

Many people will tell you there is no night in Heaven, and use the verse below as proof. But they aren't reading correctly. There will be night on the new Earth, most likely, but not in the city of New Jerusalem, because that is where God will be. There is also a great tree in the city, which bears fruit every month! There is time in Heaven, obviously, and there would have to be night in order for a day to be complete, correct?

And there shall be no night THERE (in the city); and they need no candle, neither light of the sun; for the Lord God gives them light: and they shall reign for ever and ever. (Revelation 22:5)

It also plainly teaches that God creates darkness (as in night time) in one verse of The Bible. He created the night and the stars, anyway! So it's not like it's a curse. Satan just made it like one. So yes, there is day and night in Heaven.