Koh Samui to Koh Tao - ferry times?

My plane arrives in Koh Samui at 17.10 on a Thursday. My final destination is Koh Tao. Is it possible to get across to Koh Tao the same day by boat or do I have to spend the night in Koh Samui and wait to get the boat the next day? What's an informative website giving details on boat crossings, times etc? Any replies very gratefully received. Thank you

http://www.backpackinthailand.com/gulf_ferries.html</strong>

I reckon you will need to spend the night.

Definitely have to spend the night on Koh Samui. Stay in Bang Rak, places like Mermaids, they're not too far away from the Seatran ferry and affordable, pending on season 400 or 600 Baht. The Lomprayah ferry leaves a lot further away, from Maenam.
Both Lomprayah and Seatran have early morning and mid day ferries to Koh Tao.

Samui weather blog