Ds is 6 months now but I've been back at work since he was 6 weeks (1 evening a week) I use Boots milk bags and freeze 2-3oz at a time. When we need some, we put it in a bowl and pour boiling water from the kettle over which takes around 2 minutes. By the time dp has rinsed out the bottle with boiling water it's ready, just give the bag a shake and be careful because the outside of the bag gets hot. There's still some waste but that's more because he doesn't like bottles much! I would have 2oz prepped and be prepared to "waste" it, then defrost more as needed.
It lasts 6 months in the freezer so we now use it to make up his weetabix, baby rice etc and to thin purees if needed. 1/2 a weetabix for breakfast takes 1oz milk, the other oz gets used for rice with lunch or the next day. I express at work around 8:30pm so have continued that the other 6 nights a week now he goes down reliably at 6:30-7:00