Here is the other post that I detailed the abomination of desolation clearly happens on Passover, and a future Passover date as that.

Thread: The Abomination of Desolation Happens On Passover! (100% Sure of It!!!)

In Daniel 12 it mentions there are 1260 days and 1290 days from the abomination of desolation. Thus, that 30 day difference is between the 1st Passover and the 2nd Passover.

The reason why there is a second passover is that if the dead bodies are touched on the 1st Passover, they are not to keep the feast of unleavened bread at that time, but instead 30 days later on the 2nd Passover. (This is directly related to the two witnesses dying on the 1st Passover.)

And then we see something in Ezekiel that relates to this!