Rotators are devious and deceitful. Especially if you break them down and manipulate their constituents. The don’t like that, and rarely will you get the result you want.
Here’s what I came up with and it works fine:
Just AddLocalRotation before saving the target rotation. Since you start the timeline right away, it will set the initial rotation in the same frame, so you won’t be able to see the effect of AddLocalRotation and it seems just fine.