Refers to the way that time
estimates tend to go out the window when tweaking
or finishing something up. Tends to be a 1:3 or 1:4 ratio with actual time spent. Tweak time begins when you're getting ready to go home
to your loving Significant Other
. Since you are dutiful, you grab the phone
and say "I'll be home in an hour. Can I get you anything?" Then, since it only takes you half an hour to get home, you decide to...
and you find yourself rolling up to the door four hours later, shuffling and staring at your feet like a goof.
You can also be the victim of tweak time. Any time your co-worker says, "You can have that in 5 minutes -- I'm almost done", ask him/her if that's real time or tweak time. If s/he looks at you blankly, s/he has no self-knowledge and you'd better go get a coffee, 'cause you're gonna be waiting.
See also "The last 10% of the project takes 90% of the time."