When a recipe calls for room temperature eggs, butter, etc., the best way to do this is to leave the items out on the counter for 30 – 60 minutes, depending on what time of year it is. This is pretty safe to do for 60 minutes in the cooler months, but in the warmer months, 30 minutes should do it.
Butter blends/mixes much easier when you let it get to room temperature. I sometimes nuke it, but more often then not, I accidentally melt it instead!