It would be hell imho. I worked 2 '9-5' jobs for a brief moment in my high school years; strawberry picking in the morning (5-14ish without break) and working in a distribution center (16-1ish with a break); that was hard, but it made a lot of money and was mind numbing so I was doing assembler in my head (ah to be young :) and writing assembly / drawing game sprites on scraps of paper in my pocket. It was ok.
Many years ago (<2000) I worked on one fulltime job remotely and then had another fulltime in the evening; that was coding; Java during the day, Delphi in the evening. That was extremely hard; no time for your brain to let up and (my pet peeve) you cannot walk during coding, wrecking for your body. Although I did sports for 1 hour in between, it didn't really help; because your mind is spinning all the time you cannot really relax. Also sometimes one job (because of the nature of programming), jobs bleed over into eachother; you will have missed a mini deadline for job 1 and then you will have to either tell them you're late or job 2 you're late; strawberry picking or distribution centers have no deadlines as such.
Offtopic;
What I took from it is that when I first worked those hours; a) it was physical work which kept my body ok (strawberry picking is hell on some people though; I didn't mind it) b) because my programming target (MSX with Z80) was completely kept in my head; all assembly instructions (I still know most of the hex codes and all assembly codes), VDP (video display proc), relevant parts of the BIOS and sound processor instructions were easily kept in my head so I could code during walking. This became impossible around the end of the 80s.
Although I do still program the MSX (and others) for fun, my personal goal is not to go back to the 80s but to make programming in my head possible again. Not sure if i'll ever get there but I will die trying.
Many years ago (<2000) I worked on one fulltime job remotely and then had another fulltime in the evening; that was coding; Java during the day, Delphi in the evening. That was extremely hard; no time for your brain to let up and (my pet peeve) you cannot walk during coding, wrecking for your body. Although I did sports for 1 hour in between, it didn't really help; because your mind is spinning all the time you cannot really relax. Also sometimes one job (because of the nature of programming), jobs bleed over into eachother; you will have missed a mini deadline for job 1 and then you will have to either tell them you're late or job 2 you're late; strawberry picking or distribution centers have no deadlines as such.
Offtopic;
What I took from it is that when I first worked those hours; a) it was physical work which kept my body ok (strawberry picking is hell on some people though; I didn't mind it) b) because my programming target (MSX with Z80) was completely kept in my head; all assembly instructions (I still know most of the hex codes and all assembly codes), VDP (video display proc), relevant parts of the BIOS and sound processor instructions were easily kept in my head so I could code during walking. This became impossible around the end of the 80s.
Although I do still program the MSX (and others) for fun, my personal goal is not to go back to the 80s but to make programming in my head possible again. Not sure if i'll ever get there but I will die trying.