When it's cold you don't have to change the milk or water that often. You want it to eat up all the sugars, so it may take 2-7 days sitting out. I leave the water kefir sitting out for a week before it's ready to drink, and the milk kefir in the frig now because I'm tired of it. It can stay there for a month or more.
The water kefir gets real bubbly if you keep the lid on really tight. The glass jars with metal hooks and rubber gaskets work the best. It's almost like champaigne that way.