hi mrswilliams- i know that this sounds like a pain in the ass but if you are just trying to establish a routine for you ds you need to try and stay at home with her for a week or so so that you can stick to your routine more easily. if she adapts to it really well you might not need to do it for this long.
as all us E.A.S.Y mums will tell you its easier to schedule yur life around the routine. for example my 12 week old ds is on 3 hour easy. he has a feed at 7, 10, 1. i nap with him after his 7 feed. shower and get ready after his 10 feed ( while he naps) then go out and do what ever i need to do after his 1 feed then i make dinner after his 4 feed. its not always possible to do this but once you get used to it its alot easier to do. also if your lo is on 4 hour easy you have longer between feeds.
if your lo wont go longer than 3 hours try increasing te time between feeds by 15 minute increments. ie feed at 7.15 for a few days (try and put her off with a pacifier) then when she is happy with this increase it to 7.30 etc. it may be easier for her this way as a 24 week old should be on 4 hour easy.
also are you going to be starting solids soon?
HTH