Steel Path Defense

[SomethingLog]

Often during steel path defense incursions squads will finish the defense mission before the acolyte even spawns at all. This happens even with frames that don't clear super fast. Either make those *@##$es spawn sooner or just remove defense from the possible incursion mission types.

[HunterDigi]

I know right...

So infuriating, waited so long... just for it to spawn after I killed the last enemy and it finished mission.

[MystMan]

Depends on the Defense map.  Some are built in a way that the spawn locations are spread out and far, you will definitely take longer than 5min to clear all the waves. This ensures you will reach the Acolyte's RNG spawn moment (between 4-6 minutes, and even then they do not spawn 100% of the time). 

Smaller defense map with closeby spawn points are cleared quite quickly.  Only way to drag those on is to leave an enemy alive at the end of each wave, operator void dash them away to delay the end of a wave. (or use any crowd control ability if your frame has one).

But honestly, if you want to farm Acolytes, you don't have to do so only in Steel Path incursion missions.  They spawn in any non-assassination Steel Path node, including open world maps. 
Just do a Steel Path Capture mission, run around mindlessly killing stuff and capture the target, take your time in doing so as long as the mission reaches 6 minutes then leave, whether he appeared or not. Rinse & Repeat.