I took 70 mg of Vyvanse, (lisdexamfetamine) prescribed, at 11:00 am today. Will this keep me up late (after midnight) tonight?

Possible. You are taking the upper dose range of Vyvanse (lisdexamfetamine) which is generally to be given early morning so as to not interfere with sleep. Typical washout of Vyvanse (lisdexamfetamine) is 6-8 hours with some people metabolizing (eliminating from the system) the med sooner and some taking longer. You may experience insomnia. If so, please discuss timing of when you take the morning pill with your prescribing doctor.