Melatonin- how much and when to feed?

I want to start our steer on melatonin to see if it will help him calm down at shows- I just don't know when to feed it (morning or evening?) and how much. He's 850 lbs. also, is it ok to feed melatonin along with peace pellets? I only plan on feeding the melatonin a few days leading up to the show and on show day.

VC gave you some good info on feeding it in your earlier thread, I'd start there.