You can do a simple google search for Nisan 14 30 ad and see Nisan 14 began at sundown Wed Christ dies at 30 on Thurs (still Nisan 14)
Jesus was born during the time Herod the Great was a live, Herod the Great died in 4 BC, that means Jesus was born before 4 BC. We don't know how old Jesus was when He died, He began His ministry when He was "about 30" (says Luke) but "about 30" could mean He was 29 or 31 for example; we also don't know how long His earthly ministry lasted, it was at least three years; but it could have been longer (Scripture doesn't say, that John's Gospel mentions three Passovers doesn't mean those were the only Passovers that occurred during the time of Jesus' earthly ministry).
So latching onto AD 30 is entirely arbitrary here. The exact year of Jesus' birth is unknown. The exact year of Jesus' death is unknown. A time frame of about 6-4 BC for His birth, and late 20's/early 30's AD for His death are about as close as we get.
What is clear is that on the first day of the week Jesus has risen from the dead and while on the road to Emmaus Jesus, incognito, starts walking with some of His followers and we read that "it is the third day since these things (Jesus' death)" That gives us this: Jesus was crucified on the sixth day of the week, Jesus was in the grave on the seventh day, and Jesus rose on the first day.
If that's a problem because it doesn't fit what one wants "three days and three nights" to mean (and the point here is the analogy with Jonah being in the fish, that's the point) then we have roughly two choices:
1) The first choice is that the Bible is straight up wrong and Jesus was in the grave longer than the three days recorded in the Gospel texts.
2) The second choice is that the Bible is right, that Jesus was crucified on Friday, and raised on Sunday; and trying to contort "three days and three nights" to mean something other is wrong.
Me, I go with the second choice. Jesus died on the sixth day of the week, what we call Friday in English; and He was raised on the first day of the week, what we call Sunday in English. As the Gospels themselves say, and as the Church has always understood and believed.
-CryptoLutheran