It really depends on your goals and personal preference. If I want to get in say 20 minutes of cardio, I usually start sipping my shake during the end of my weights and it's mostly gone by 5 minutes into my cardio. I'm on a lean bulk though, and so I'm not trying to burn any fat, just keep it off. I find the shake doesn't hurt my cardio performance, and this way my muscle will be reloaded with nutrients sooner.