spare time and full time

It depends on your company’s hourly over time rate, because some do give out good over time incentives, while others are just a little bulk up for your paycheck. This also depends on the project or workload your company is in need for manpower overtime working and depends on what type of company you are working with. If you are in the industrial work space, well they do give some decent amount of overtime pay, If you are in the corporate and commissioned type of work, well expect some add kick-back on your pay slip.

I think it would be better if you can have both a full time job and a part time one. But personally, having a business of your own will give even higher earning.