Scalding covers quite a large range of temps - something at 60 would probably be scalding. A food thermometer would give you a definitive answer but the water is probably 'only' at 70 if you've boiled the full litre. Boiling less would take less time to cool (1 litre cools at 1C per minute).
andrea the nurses are wrong, you should report them. They are quite clearly not following the NHS guidelines and there are special guidelines for HCPS unless they are using a special formula which can't be made with hot water. In that case the risk of using non-sterile powder is smaller than the risk of using the 'wrong' formula.
chocolate you should report your HV too. HCPs giving incorrect advice should be targeted for retraining.
You can still make in advance, it's just not ideal.
Hot water + powder = dead bacteria
Cool and serve immediately = no time for any survivors to reproduce to harmful levels
Cool and store in fridge = bacterial growth inhibited, approx 24 hours before levels approach harmful
Cold water + powder = still living bacteria breeding and therefore reaching harmful levels potentially almost instantly given the rate of reproduction at room temp and almost certainly within the recommended time to discard the bottle.
Once sufficient levels of the bacteria have been introduced into the system they will continue to reproduce, causing gastroenteritis. A slightly leaky digestive system could allow them to enter the bloodstream causing sepsis, and potentially entering the brain, causing encephalitis. The risk is greatest for tiny babies, but gastroenteritis is no picnic for anyone.