That’s because the Set Timer’s delegate requires none:
It will happily register with the CustomEvent but not with the CustomEvent_0 as its signature (bool) is not matching that of the timer (none).
Were you to bind something that requires a signature, the member list will be generated correctly, and automatically:
Essentially, the system prevents you from accidently binding to something that makes little sense:
The Set Timer node has no clue what Overlapped Actor / Other Actors are.