Would this work? Making up bottles in advance.

I know what the guidelines say but I can't think of any reason why this wouldn't work. It's how I used to make bottles for my neice when she lived with us as a baby.

M, for example is on 5oz. Can I make up a bottle of 3oz of water but with 5 scoops on milk. Put it into the fridge. Then when it's needed, add the other 2oz of boiling water making the bottle ready to drink instantly. The formula would then have been in contact with hot water twice...

I wouldn't add the powder - formula should be used within 2 hours once the powder is added.

I would fill bottle up with 3oz of water (that has been boiled in kettle then left for 30 mins), leave at room temp and then add 2oz of boiled water (cooled for 30 mins) when you are about to use it and then add the powder. You might actually only need to add 1oz.

Lily has 6oz bottles - I just fill them up with 6oz of water (from kettle that has boiled and then been left for 30 mins), I then leave them on the worktop at room temp. I add powder when Lily is due a bottle and then warm either in a jug of boiling water or in the microwave.

when girls were babies - they're 3 now - we used to make up bottles with boiling water, then put them on the side. We'd add milk powder and warm when needed.  I think the current guidelines want milk added to hot water to kill some very unlikely bug. But I'm sure someone can give you more scientific advice.