Would be best to save it in the vessel you are going to ferment the starter in, like if you had several Erly flasks. Do your boiling in the flasks to sterilize the inside and it's contents (starter wort). Cover, cool to room temp, refrigerate for no longer than a week I'd say. Warm to 80 deg or so. Pitch yeast.
You may be able to store it more than a week but with a cup of sugar water in a home environment, like a fridge, organisms begin moving in almost immediately.