I was wondering the exact same thing as OP. I wanted to move my Timeline to a function (with a bunch of other nodes, not JUST the timeline…) for re-usability reasons. So I tried Collapsed Graph as you mentioned… but it turns out you can’t really call a Collapsed graph more than once (as opposed to functions). Which basically brings me back to square one again…
In the end I had to create a custom event in my blueprint, and call that event inside itself… which kinda feels like a hack.
I still don’t get why you can’t have Timelines in a function…