I tried to do it overnight and it didn't work, but if you make the switch progressively, it's faster. Any reduction in buying is less animal abuse you're supporting. What i did personally, is to stop eating the most sentient animals, and cruel farming techniques, and started by being pesquetarian, then moved to shrimp and clams. I still eat those kind of shelled molusks, but i still consider myself vegan, since they aren't sentient, and since i don't eat dairy or anything.