Almost, but not quite - if the difficulty increases by 18%, then the time to reach that change will be 18% less than 2 weeks. (because the 2016 blocks were found 18% faster).
Close, but it's actually 1/1.18 ~ 0.85 or 15% less than 2 weeks. 100% increase would be 50% less, or 1 week etc.
Good catch, I stand corrected.