It becomes an issue if it takes more than a day. Scrum, Kanban, RUP, XP, waterfall - whatever "methodology" they say they're following, it boils down to "tell me how long this is going to take and I'll check to see how close what you said was to the time it took". If you can make a change in an hour, sure. If it takes a day, it's going to break your "commitment".