I did two full-time jobs for a month as part of changing jobs fifteen years ago and it’s exceedingly intense but otherwise was fine; eighteen hour waking days leave a lot of boredom time, no matter how many hobbies you have. Employers don’t like this because that’s a lot of work they could have persuaded an employee to provide as unpaid overtime labor instead; much this outrage is simple jealousy. If you’re doing the job to the specifications requested at a sufficient level to remain employed, then they have no basis to cry outrage. Employment is just as monogamous as marriages are: sometimes, not always.
> eighteen hour waking days leave a lot of boredom time, no matter how many hobbies you have
Lol - you don't have enough hobbies.
24-18 = 6 hours "non-working" time. Eating, washing and shitting is min 1 hour/day.So 5 hours of bed time with around 4.75 hrs of sleep at most, because we don't fall asleep right away.
The math doesn't work long term. It may be kept for 1-2 months even when a person is 21 yrs old, but I doubt it it can be sustained more than that.