2-3 days. No longer than a week, or 7 days. If soreness lasts longer I would have it looked at.

Its not like the whole muscle is "sore" per se, its just a little tender where the needle went in because it ripped apart some muscle that must now heal itself, so naturally it will be sore for a bit.

Usually, when I hit a vein or blood comes out after 'jab the injection site tends to be a little more sore longer, which I am assuming due to broken blood vessel or vein.