If I am forced to provide estimates without enough time to properly investigate the subject at hand I tend to massively overestimate. The fix is almost always more difficult than I think it is going to be. If I think something will take a day then I say two days. If I say something is going to take an hour then I say a day. What I am trying to illustrate with these comments is that for all but the most mundane tasks like spelling mistakes, even a small code change can explode into a full day. For anything I think might take a day or more I double the estimate. I know it can be tough to do this. Management wants small numbers. You want to look smart and capable in front of other developer. See also Scotty Factory.
Even if you have QA team members that will test your code you have to remember that it is your job to test the code as well. Make sure to factor that into any estimate. That is something I have seen a lot of developers leave out of their estimating process.
