The latest NHS and WHO info says you should make each bottle up with water at a MINIMUM of 70 degrees. It's not leave the water for 30 mins, it's leave it for no more than 30 mins so you don't end up with water less than 70 degrees c.
The only problem with using boiling water is that you may have to cool the bottle (depending on how good you are at mixing the right amount of cooled boiled water) and sometimes bottles warp if you out boiling water in.