In case the MTP of the tip of the chain is 12h or more after the MTP 6 block before the tip, the proof of work target is increased by a quarter, or 25%, which corresponds to a difficulty reduction of 20%.
So as long as the BCC keeps lagging behind massively (less than 6 blocks every 12h) the difficulty is reduced by 20% after every new block.
[1] https://github.com/Bitcoin-UAHF/spec/blob/master/uahf-techni...
So it takes 6 consecutive blocks to be found "fast enough" (that is, within a 12h window) to return to the normal difficulty algorithm.
Furthermore if they really only wanted to slow down BCC and nothing else it still wouldn't be very efficient. They'd just postpone the scaling for the next 6 blocks and then the rule would kick in again. So they'd have to keep make sure that they're always just at the limit of 6 blocks per 12 hours... but at this point you're actually mining block and contributing to the ecosystem, so there's no problem.
Looks like though they're getting blocks now, 4 blocks in less than two hours.