As Jonah was in the great fish, how long did Jesus say the Son of Man would be in the earth?

Answer: Three days and three nights

As Jonah was three days and three nights in the belly of the great fish, so the Son of Man would be in the heart of the earth.

“For as Jonah was three days and three nights in the belly of the great fish, so the Son of Man will be three days and three nights in the heart of the earth.”— Matthew 12:40 (BSB)