You have to kill the whole other team before they respawn back. The respawn time will take longer as the game gets longer. Timer also can reset after both teams have fully respawned (I think), causing the time to respawn to go back to being around 5 seconds. Game ends when the whole of the other team (or yours) is eliminated/killed. The diamonds on the corner indicate how many of each team are left alive or dead.
It took me a long time to know how it even works, but after some testing (and info on pelican discord) I think I kind of understand it now.