You'll be super busy with law school, focus on that, make sure that's a priority, do your best and finish top of your class.
That said lots of people build their idea with full time jobs, while going to school and even with a family.
So make the most of your spare time, weekends, summers.
Whether you learn to code or are a co-founder it's going to be work.
This will be interesting for you: http://www.startupsfortherestofus.com/archives
And I love @DHH's advice here: https://www.youtube.com/watch?v=0CDXJ6bMkMY
Good luck, make the most of it.