Jon Simson, executive director of SoundExchange, told members of Congress and representatives of webcasters yesterday that webcasters who were in compliance with reporting rules and were in negotiations with SoundExchange didn't need to shut down in light of new royalty rates. However, this did not constitute any sort of "promise," as was originally reported here, but more of a summary of webcasters' options going forward.
Payments under the new rates are technically and legally due on Monday. But if webcasters don't pay, SoundExchange will not demand payment or force them offline, since rates negotiations are ongoing. Instead, any fees mandated by the CRB decision that remain in place after SoundExchange and webcasters finish their current negotiations will be due retroactively to July 15th, plus interest.
I posted a summary of what this means for large versus small webcasters here (large webcasters could be affected the most, since the CRB's flat per-song-per-listener rates are not up for negotiation).