Just an odd trick (in particular for Seed Bearers) since we're on topic... the game seems to count damage dealt to the boss only after your Squads are done attacking. Which means you can do a Weak attack and let it run without Fast forwarding/skipping, until you deal the last hit people should still be able to join in (even if you know your final total damage will kill the boss, the game doesn't calculate it beforehand). Incidentally, this is the most likely explanation for when Raid damage total exceeds the Boss HP by far.

Just tested it with two alts, and it works. Just use tanky, low-damage first few squads (for that matters, for Seed Bearers, a single maxed 4*+ can probably solo it, given enough time) and let the battle run while you do something else