If by full time you mean the American definition of 40 hours, then you can do it by working 80 hours a week divided by the number of days a week you work. So either by working 11.42 hours 7 days a week or working 13.3 hours 6 days a week or working 16 hours a day 5 days a week, or working 20 hours, 4 days a week. It's impossible at 3 or fewer days a week because you exceed the physical limit of 24 hours a day. To quote Marx in Value, Price and Profit:
[...] the length of the working day is also limited by ultimate, although very elastic boundaries. Its ultimate limit is given by the physical force of the labouring man. If the daily exhaustion of his vital forces exceeds a certain degree, it cannot be exerted anew, day by day. However, as I said, this limit is very elastic. A quick succession of unhealthy and short-lived generations will keep the labour market as well supplied as a series of vigorous and long-lived generations.
If by full time you mean the American definition of 40 hours, then you can do it by working 80 hours a week divided by the number of days a week you work. So either by working 11.42 hours 7 days a week or working 13.3 hours 6 days a week or working 16 hours a day 5 days a week, or working 20 hours, 4 days a week. It's impossible at 3 or fewer days a week because you exceed the physical limit of 24 hours a day. To quote Marx in Value, Price and Profit:
source: page 29 of this PDF
So yeah, it will literally KILL you but you can do it... for a while.