It wasn’t meant to. Nighttime is night time, the time of a day (darkness) within which there’s darkness.
Daytime is the time of a day within which there’s light.
It’s common usage now and then to refer to daytime as a portion of a day. That’s way we all know what’s meant by the usage of daytime versus nighttime. It’s common.
On the otherhand, The phrase “in the belly of the Earth” has no common usage that I am aware of now or in the 1st Century occupied Jewish culture (which is what really matters). People have speculated it meant in the tomb. Maybe, but I doubt it if you actually read Jonah’s prophecy.
I believe Jesus’s distress (1st night) began in the Kidron ravine (that runs from the Temple to the Dead Sea) the 1st night in fulfillment of Jonah’s prophecy whereby Jonah’s distress also began before he ever entered the fish.
So they said to him, “What shall we do to you so that the sea may quiet down for us?” because the sea was growing more and more tempestuous. And he said to them, “Pick me up and hurl me into the sea so that the sea may quiet down for you, because I know that on account of me this great storm has come upon you all.”
Jonah 1:11-12 -
https://www.biblegateway.com/passage?search=Jonah 1:11-12&version=LEB
Clearly a type of Christ’ Distress.
Not that you’ve said there is, but there is no conflict with what Matt 12:40 and aThird Day resurrection if you understand ‘the belly of the Earth’ to begin prior to entering to tomb, at Jesus’s distress that 1st night. If you understand ‘the belly of the Earth’ to be His entombment, there is conflict, IMO.