I used
Darian Culbert to book my last minute Halong Bay cruise and he got me a pretty good deal on Phoenix Luxury Cruise for the price of a deluxe leaving the next day. Arranged the transportation and everything too
He might know about other cruises for Bai Tu Long Bay too.
Best deals are via email especially for last minute cruises. Very easy to deal with.
Would definitely not recommend an one day trip unless absolutely necessary.