I just wondered if we are sterilising right, bethany is only 5 days old so we are still learning, we have a tommee tippee electric steriliser, which says bottles last 3 hours if unopened, so rather than sterilise one bottle at a time, how do you sterilise more??? because cant put the water in straight away as midwife says water must be hot to mix the milk powder. So we're unsure what to do???