Got in an ongoing silver game twice two days ago - both times the same host.
There was absolutely no delay between waves, even the audio commentary from the commander/shuttle pilot didn't play out completely before the new announcement for the new wave began.
Also, enemy density seemed extremely high even in the first waves - add to that the fact that apparently all spawn points remained active constantly even if you stood right in one. Wasn't funny killing some mooks only to be downed instantly by the fresh group spawning literally 3 meters behind you.
Host was a Turian Ghost with a Carrier, so he didn't have as much issues with being focused I imagine...