Malaria prophylaxis is dosed -once- a weeek. Half-life 60-70 hours. Covid treatment is -twice daily-.
The therapeutic index of chloroquine in the treatment of covid-19 is relatively high. Some people take chloroquine or hydroxychloroquine at about half the acute dosage used for covid-19 (autoimmune disorders) for literal years.
Given the half life as you mentioned, once or twice a week with enough lead time would be a sufficient dosage against covid-19 too. It's just that if you want to reach the concentration of chloroquine that you would have to take it over a long time otherwise, you need very high doses. And since you're already infected and have a ton of the virus, you also need higher concentrations than for prophylaxis.
plaquenil on the other hand does have a higher therapeutic index.
The other major disadvantage is that these drugs can interact with protease inhibitors.
What are the possible consequences of this?
Kaletra, a protease inhibitor, is a combination of two drugs, one of which is a CYP3A4 inhibitor. It is used with some success on coronavirus patients.
Co-administering this with chloroquine 500mg/BID could easily result in chloroquine concentrations well above LD50.