1. SOA and SRV records used for discovery have to specify TTL; Section 6.1: https://www.rfc-editor.org/rfc/rfc8765.html#section-6.1

2. A standard nonzero TTL is otherwise not very meaningful as long as subscription is active. Section 6.3.1 explains the TTL field of a PUSH message clearly: https://www.rfc-editor.org/rfc/rfc8765.html#section-6.3.1

But this mechanism does not replace normal DNS, only supplements it, so no, you probably still need to set TTL.