I know you're likely just going along with what the lfs says, but take it slow - nothing in this hobby happens quickly. Most new systems need a few weeks to cycle before adding livestock....so take your time...it doesn't sound like you've experienced much of a cycle...yet.
Anyhow, it depends on what lights you are referring to. If you have lunar or moon lights, you can leave them on or put them off before you go to bed, if you mean the blue actinics, they should go off with your main lights. Just remember that you don't want the tank too bright....it would be like sleeping with the lights on for us...