I've done Semidar spawn a few times last week, the spawn times were within 29-32 minutes each, solo with a wammie (wraith form). but I haven't done a spawn other than that since before primers came out.Try it with the new changes. I'm telling you not even remotely possible. Best time I've had is 38 minutes and I assure you I'm no slouch nor is my gear
I have done semidar spawn in 18 minutes solo before, my average time was closer to 20 minutes per spawn though (from spawn-pop to champ down).
I didn't really farm barracoon much, since they added Replicas to champs, but Barracoon "Spawn" is much weaker than Semidar spawn.
I don't think 20-25minute solo spawns with the changes over the last year or two are out of the question.