I had a problem described to me a few weeks ago.
After a few moments of thought I answered, "I know what the problem is and how to fix it. It will only take me a few minutes BUT, they way they are using the application is not covered in the signed off use cases and there is no specific test for this set of operations. That will take 2-3 weeks to draft, get approved and fully regression test the fix and get the customer to sign off on it".
The PM answered, "But I told the customer thay could have the fix tomorrow. It didn't sound that difficult to me."
The PM is a failed developer which says a lot really.
The moral is that changing one line of code may only take 10 mins but everything else could make the time to fix extend out for weeks if not months.