Tested with Orca Slicer and X1-C, you can avoid your tricky timing step. Here’s how I do it:
1- In slicer, use cutting tool to cut your model horizontally in two parts, one part for each color. For upper part, check the “Place on cut” checkbox. Also enable “Cut to parts”.
2- Assign a filament for bottom part and another one for top part. Also enable the purge tower.
3- Add a “Pause at layer” where color change is needed. No need to add a filament change command.
4- Slice. In Preview tab, use slider to observe filament change at appropriate layer.
5- Print.
6- When the printer pauses, from printer control panel, close the “Pause” dialog then unload old color and load new color. Optionally, perform a few manual extra extrusions to flush out old color.
7- From printer control panel, hit “Resume” from homescreen.