The best spare time business is an online business. You can start one within a few hours and operate it from anywhere in the world. As long as you have a decent computer with an internet connection. Simply start off with buying a domain and pick/create a product.
Why an online business is the best spare time business. Is because everything we do online is digital. We can have web pages working for us 24/7. And the work we put in is permanent. You can start with working one hour every day. Just make sure to get some form of education and guidance.
If you take some time and learn, it’s pretty easy to create series of web pages & online systems that sell our products for us. Get this done right and you will have lots of time to duplicate and improve.