The most up to date advice is to make up as needed. The main reason for this is a bacteria that can grow in formula powder so you have to add hot water thats at least 70c to the milk powder to ensure the bacteria is killed off. I make up the bottles like that then rapidly cool them (stick them in a jug of ice water) and then stick them in the fridge. I only make 2 at a time but they would be ok in the fridge for up to 24 hours. If im out and about i would take one of these bottles if DS feed was due in the following hour, any longer than that and I use a ready made carton.
The best/safest thing to do is make up as needed with hot (70c) water and consume within an hour or two.
If occasionally you need to make up a bottle in advance, make it up with hot water, cool, and store - use as soon as possible but definitely within 24 hours. Not as safe as making as needed but still acceptable.