It took me a little while to work out my system, but now here is what I do:

I use an electric steriliser, so wash bottles at night after she has gone to bed and sterilise them. Then I'll take them out once it switches off and part fill the bottles with boiling water (she gets 180ml bottles so I put 100ml in). Put the lids on the bottles and then pop in the fridge. When it comes to feed time I add 80ml boiling water to the bottle (the other water is now fridge cold) and it brings it up to the right temperature, add formula and feed! I used to make up the bottles fresh everytime, but I too found it awful waiting for the bottle to cool down while I had a screaming hungry baby in my arms! It's also handy with night feeds, don't have to stand around wasting precious sleep time waiting for a bottle to cool!

i did try filling the bottles with 180ml of boiling water and leaving them on the bench until ready for a feed, but found she didn't like it quite that cool (over winter our house gets quite cold especially overnight).

That's what worked best for me, as i said it did take a little while to find the right way for me to do it, but once you nut it out and figure out what works best for you, you'll be fine! I think as long as the sterilised bottles are used within 24 hours it'll be fine. If DD only has 5 bottles in one 24 hour period, even though i still have one left over (my steriliser does 6 bottles at a time), I'll still empty it out, re-wash and re-sterilise.