How long does it take for fermenting to complete?

An interesting question. the question requires a complex answer, but I'll try to get it clear. There are two fermentations to make an alcohol drink. Primary fermentation in vats, or open barrels and secondary fermentation after the 'must' has basically stopped fermenting. Speed of primary fermentation which is what I think you refer, depends on the type of yeast, if you add any or not, or if you let it ferment naturally. Also, the amount of sugar in the fruit or 'must' you are fermenting makes a difference. The more sugar, the longer fermentation takes and the more alcohol produced. You can stop the fermentation in the middle by cooling the 'must' and this will make a sweeter wine or drink and also begin to complete the process sooner.  more