I don't follow the official guidelines but HV said I was doing it as safely as possible without following advice.
I make enough bottles up to last 24 hours and store them in the fridge.
I use little pots designed for taking formula powder out and about, and measured the powder for each bottle into the individual pots. It saves the scoop getting steamy and clogged up when tipping powder in over hot water numerous times.
Boiled kettle.
Bottles already scrubbed and sterilised ready to use.
Pour boiling water into bottles, then tip the formula into each bottle from the individual pots straight away. Formula going into boiling water kills any bacteria.
Put teats on, then unscrew and re screw teats to release any trapped steam.
Lids on, shake thoroughly.
Leave out on kitchen counter until completely cooled to room temp. Usually about an hour.
Store in the fridge.
If going out I would take bottles in a cool bag with an ice pack and flask of boiling water for warming up.
I would warm bottles up as required and use them up within 24 hours.
I have two full sets of bottles so one is in use and there is always a clean set in the closed steriliser ready to use.
I do it this was as I find it easier to warm up a pre made bottle up, rather than make each one from scratch then bring down to a suitable temperature.