[Malleus Dei]

My wife is a highly-paid (IMO quite overpaid) expert, who works on far more complicated software every day, and part of her job is estimating how long something will take to change. Even when she hasn't seen the code. She's very good at it.

The exceptions are when she encounters bad code, and she then rewrites the code, sometimes from from scratch. She recently rewrote something that makes OOTP look like "Hello World," from scratch, in eighty hours. She was Hell to live with while doing it, though.