according to jps_ in the ethermining subreddit, the ice age stops at 20 seconds.
*difficulty bomb creates a different equilibrium point because it is now adding about 1/2500 every block, and the adjust is in units of 1/1024, so there is a meaningful increase in difficulty, which needs to be offset by a meaningful number of blocks getting solved >18 seconds.
This basically means that difficulty will increase until average block solve time is just over 20 seconds.*
There is a bunch of other great info about the ice age released to explain yesterdays spike in difficulty.
I urge you all to check it out.