How long will it take to feel an energy boost from Re-Lyte Boost?

It'll take around 15 minutes.

Each serving of Boost contains 120 mg of caffeine from green tea extract. As you probably know, caffeine gives you a pretty quick energy boost. Caffeine from coffee or soda typically starts to hit you within 10 minutes. Since Boost is a powder, absorption takes a little longer than that. That means you'll take a little longer to feel the initial effects—around 15 minutes or so.