I always followed the rules exactly with formula - not "everyone" ignores them.
There is a most preferred method - every bottle made fresh by boiling one litre of water, leaving to cool for 30 minutes, mix, cool and serve. Discard any remainder after two hours max (though for a younger baby, I preferred to discard after less time than that to be extra safe).
Then there is a second option endorsed by the WHO and health authorities - it carries slightly increased risk but still advised and perfectly safe in real world circumstances. Make up as above and flash cool the bottle really quickly - I put the bottle deep in a bowl of ice cubes and run the cold tap over it all for a couple of minutes. Once cool, transfer immediately to the fridge and store at the back of a fridge shelf, not in the door. It can be stored there for up to 24 hours (but I prefer much shorter time personally of max 12 hours).
To heat, I put the refrigerated bottle into a deep cup of boiling water for a couple of minutes and test the temperature before serving. Again, advice says discard two hours after heating but I always erred on the safe side and discarded after less time if using this method.
If you are taking the bottle out with you, it needs to be stored in an insulated bag with an ice pack until ready to be heated.
It sounds like a whole lot more of a nuisance when written down than it actually is.