I have been to the thieves guild and some theif (can't remember his name) wants to meet me at the Splurging Sturgeon for some heist. I have been there to find him but he is nowhere in sight. I remember he said something about dusk. Does the time of day that I go there matter? Is that why he isn't there?

you most likely need to wait until dusk to find him.. i know in BG2 it's like that for certain quests.

Also, you can only have one member of your party meet him. I like to send all of my party members into the tavern except one. Maybe that helps?

Wait till night to meet him, and have ur main Character meet him. Leave all other members in the in. Have fun, you'll get some good kicks n money out of this quest.