Weekly Effort.

Under two hours a week, often far less. Set it up once and it mostly runs itself, or you dip in only when you feel like it. Don't expect a real income, but the time cost is close to zero.

A few hours a week, fit around a full-time job or school. The most common time budget on this whole list, and where most realistic side income actually lives.

A real second job's worth of hours. Usually means you're building something, an audience, a client base, a catalog, that keeps paying after the initial work.

As many hours as an actual job, because for a lot of these, it basically is one, just remote or on your own schedule instead of in an office.