Concerta is a stimulant so it’s immediate. It may take a few days for your body and mind to get used to it though.
Here’s more on understanding ADHD medication:
A Patient’s Primer on the Stimulant Medications Used to Treat ADHD
Penny
ADDitude Community Moderator, Parenting ADHD Trainer & Author, Mom to teen w/ ADHD, LDs, and autism