Sterilising-Im confused

[valz]

I have a tommee tippee electric steam steriliser, it has a countdown timer and the instructions say if the contents have not been used within 3 hours they need to be sterilised again. why is this? my twins feed roughly every 3 hours so i only need two bottle/teats every 3 hours which means turning on the steriliser with all the same bottles in it every 3 hours, i dont understand how they dont stay sterile. Is this the same with every steriliser?

They become non-sterile the moment you open the steriliser lid so it's rather OTT IMO.

Do you wash the bottles etc in a dishwasher? That should be plenty.

assemble the bottles after sterilising and they will be ok for 24 hours.