I agree Shani, they are fantastic for veggie's, you can get them a perfect crisp tender (as we prefer) with experimentation. I'd be lost without my B&D Handy Steamer for rice too. Since we moved into our house I haven't found my cookbooks and manuals but I checked my steamers (B&D and Oster).
My Oster has a pic of corn on the cob with 25-30 min. for the time. I googled my Handy Steamer manual and it says 29-33 min. with the cobs cut to fit and stood on end in the bowl/basket.
That said, I'd have to go with Charlatan, those times seem like you'd end up with mush even though the steamers do take a few minute's to get up a head of steam.
I'd start conservative on the time and check for your preferred doneness. I haven't tried corn yet because I usually grill it when it's in season, so I don't have experience steaming it.
I don't know what you mean by what setting to use. Both of mine just have a timer knob you dial to the required amount of time for the food cooked. Maybe yours is digital and/or has more bells and whistles?