Is it legal to do two full time jobs at the same time?
Yes, it is legal in most states, but it is very hard to do especially if you have a family. I tried doing it once. I was working at a center with the mentally ill Mon-Fri 8am-4pm and then a second job of bartending Wed-Sun 6pm-2am. This lasted about a month, as I was so tired all the time and I never had a day off to rest. I ended up quitting one of the jobs to have a more peaceful life. It was well worth it. Anyway, if you can handle it and can stay awake, that’s great for you, but I didn’t like it.
It depends on the terms of your contract of employment with your employer. There are employers which allow its employees to take on another job with another company, whether it’s a full-time or a part-time one. However, if your contract is silent on this matter, then you are expected to devote your full time to your company (which means, go moonlight elsewhere at your own risk).
Legal, yes. Good idea, no. If you are a single person with no life or relationships, maybe you could swing it. If you have anyone in your life to nurture a relationship with (girlfriend, wife, kids), you will not be able to keep that going when all your time is spent working. Don’t expect anyone to feel they are tied down to you if you aren’t devoting time to them.