How long is a day on Proteus?

About 26.9 Earth hours · orbits Neptune every 1.1 days

Neptune's second-largest moon, shaped like a potato and as large as a moon can be without becoming spherical

Proteus is shaped like a potato because it's at the SIZE LIMIT for irregular shape! Any larger and its own gravity would crush it into a sphere. It's the largest non-spherical moon in the solar system!