If the grapes are white you can leave them crushed up to seven days and it will give a beautifull straw colour, if the grapes are red and white wine is desired leave not longer than 24 hours, leave longer for rose, leave up to seven days for red. No tablets required otws will kill the natural yeast in the grape skin, but a culture from the same grape can be started separetely and added later on if campden tablets are used. The adding of sugar is important as grapes grown on northern climates lacks of it. You need to try to make wine at least of 12% for keeping reason. My best regards Don Vincenzo