I do up my 240ml bottles and pop them in the fridge, then heat them in the microwave before adding formula. In my microwave, refrigerated (cold) bottles take 46 seconds to get to the desired temperature, I usually take the cap off but leave the teat on. Give the bottle a good shake to ensure the heat has been evenly distributed, then chuck the scoops of formula in and shake again.

You'll figure out pretty quickly how long you need to microwave your bottles for, some microwaves take 20 seconds, some take a minute - just play around and it'll become clear in just a few feeds how long your microwave needs HTH!