seems if I enable the additional waves timer, it overrides the kill milestone, making it where players respawn at a set amount of time rather than having both options.
edit: oh it's a known issue. hopefully I get to see it get fixed in the future, did Alpha/Delta invasion with BYOC and it worked pretty well in tandem with the score system, issue is the score system probably overwrote the hud showing how many kills/time left for the next respawn wave. I DID do this with The City of the Damned and Happy Time Circus 2 and it also worked really well with the 5 minute timer.