The 'Estimated Date' for a new difficulty adjustment is wrong.
If the hashrate is such that a 10% difficulty increase is warranted, then the previous period was 1 / 1.1 times too short. So if you assume a 10% increase each cycle, then the length of each cycle is only 12.7272 days, not 14.
This property results in a nice expression for the lifetime yield of a mining bond / equipment:
14 * D / X
(D = daily dividend/payout, X = fractional difficulty adjustment (so X = 0.1 for 10%)
Thanks for pointing this, I already updated the code.