If exercise and meditation is something that interests you, you can become a yoga instructor and offer classes at night for busy people.
Starting out you should probably take a course, even if you are already practicing yoga. This will allow you to do things in a more structured way. There are places that offer part time courses for working people. For example YogaLife in Cape Town offers yoga teacher training Wednesday evenings 7:30 – 9:30pm and Saturday & Sunday.
Once you have worked out the operational details, you need to find a venue. You should look for dance class venues, or ballet venues close to you and ask if they are willing to rent the studio to you for a few hours. You can also look for halls that are rented out for events, some organisations that own halls rent it out for cheap for the local community.
Advertising & Promotion
Yoga classes is a local business, advertise your service on Gumtree or on Facebook groups aimed at your area.