Here is my suggestion. I would create a Null Object and apply User Data to it, Float, Float, Real, and 0.001 for the settings. See image.

Go to the Timeline, select the Time Scale keyframes, and Shift/CMD, drag these keyframes to the User Data. (CMD or Control, based on your settings)

This Null object, with a good name, can be dragged into the Asset Browser.

When you need it for another scene, drag this Null object into the Object Manager, and Shift/CMD drag it to the time scale.

I'm not aware of a faster workflow, assuming you like to add the keyframes while having worked already on the new project.

Otherwise, please make a copy of that project with the Time Scale animation, empty it completely, except for the Time Scale, and store that c4d file in the Asset Browser. This will open a copy of that, but to be clear, it will not inherit its Time Scale Animation to an existing scene.

All the best