You can eat your boquerones in as little as 4 hours, but they are better left a full day. So to recap, if you want to serve homemade white anchovies, you'll have to start 48 hours ahead of time. But that's a minimum -- you can keep white anchovies in the fridge for a month and they will only get better.
I eat them plain sometimes, but they are better on good crusty bread, or as a pasta topping. Boquerones are excellent on crackers, too.
Spaniards eat them with dry fino sherry and Greeks eat them with either raki or ouzo. A cold martini would be an excellent American accompaniment.