Haven't been Eldening because I was busy working on something for a friend. Still lots of other games I want to play, too. Anyway, F2P. Got stuck on this for days. Looked up how people were doing it, but I don't have Modernia/Blanc and my Tia/Naga aren't strong enough. After experimenting, I found that the key is using Red Hood manual spam to get Full Burst quick, nuke the dangerous mobs, then either 1. Red Hood nuke the next group of mobs on the right of the Spawner and then kill the spawners without Full Burst, OR 2. use manual Red Hood spam to get Full Burst before Silence happens and activate Full Burst again to nuke all the mobs, then use Full Burst to gun down the Spawners quickly. Spamming pause helps to save time, too. Oh, and I equipped Red Hood and Rapunzel with the Cube to charge Burst quickly.
BTW I really hate this game's gameplay. So many times I'm about to clear a stage and the boss becomes invulnerable until time runs out. Or the camera moves up and I can't shoot crucial enemies at the bottom. Worst game design I've ever seen.