You could simply say, "I don't give estimates in under 3-hour increments, because there are inevitably other fire-extinguishing and support activities that interrupt even the most trivial tasks."
Sometimes I get interrupted with "Alice needs X added to Y right away", or "Bob needs reassurance that this is working as intended in the original ticket" -- no problem. Other times, one might lose productivity to things like, "Java update broke our GWT compilation toolchain completely".
It helps if your manager knows that such interruptions happen, too. I also am a fan of overbudgeting and then revising later once I understand the problem better.
Sometimes I get interrupted with "Alice needs X added to Y right away", or "Bob needs reassurance that this is working as intended in the original ticket" -- no problem. Other times, one might lose productivity to things like, "Java update broke our GWT compilation toolchain completely".
It helps if your manager knows that such interruptions happen, too. I also am a fan of overbudgeting and then revising later once I understand the problem better.