Did you know you can easily swap Hourline / Long Form Arrow Key Navigation?
It's configured in the Toolbox > Settings > Miscellaneous and you can select one of the two options:
1. Alt Key Controls Long Form
2. Alt Key Controls Hourline
For one of the timelines it is possible to use the keyboard arrow keys, and for the other timeline the arrow keys + the "Alt" key to trigger the navigation. Find out what works best for you!