Yes Miniature Schnauzers do require quite a bit of exercise to stay healthy.
You should walk your Miniature Schnauzer for at least 30 minutes every day so you need to be able to commit at least 30 minutes per day every day to walk the Miniature Schnauzer.
However depending on the Miniature Schnauzers energy level you may need to walk the dog twice per day at 30 minutes each day.
Dogs are a lot of work and a big commitment.