Boost drinks will be one of the worst things you could ever have. I use one right now, they're actually quite useful in spite of something I read on a health site. Best time is right when you get up, 1.5 hours after eating your first meal, whenever else you want, and before bed.

why is it one of the worst thing you could ever have?

Because it has a google kabillion grams of sugar and lots of caffeine. You should be having nothing with such things in it.