Looks like you are treating for Ich, fin rot or some fungal infection.
The product you are using is malachite green - there are no explicit instructions regarding duration of dosing. The dosage rate is 1 mL / 10 litres of water. You might be better off looking for a similar product with English instructions online, and then following that treatment protocol.
The only thing the instructions does say is that if you have plants, you should change at least 50% of the water "after treatment" (however long that is).
You will also want to be aware that malachite green will stain everything (silicone, hardscape, clothing, countertops, etc).