I also looked into this and seeked advice from KT.
If I am making if advance, I boil kettle, use the water within 10 mins, add powder, cool quickly in very cold water and fridge for up to 24 hours. The water needs to be hot to kill off any bacteria that is already in the powder.
Adding the powder to coolboiled water doesn't really work the same but I do know many do it this way. For night feeds make the bottle up and warm up when needed or take a flask with hot water to bed and already measured out powder and mix upstairs. If too hot just run bottle under cold tap for a couple of minutes.
No only use for bottles for an hour, then bin, it about germs breeding on the teat etc. You could have a few bottles made up with less milk but a lot more faffing especially if your never sure how much milk he is going to take for each feed.