I make up my bottles with water then just add the powder to them as he needs the feeds. Alex only has four bottles a day now, so i know pretty much when they need to be ready by, but i still make 4 bottles of water up in advance, i heat the water in the microwave if it needs doing, then add the powder & shake it so there are no hot spots.
If a feed isn't used within an hour it is meant to be thrown away, although i've someyimes left it for another 10 mins or so if he hasn't finished yet, not that is usually a problem as he drains 9oz's pretty quick, now!!
When Hannah was a baby i made her milk up, put them in the fridge & heated them up when needed, & she was always fine, but i find the way i do it now to be easy enough.
