Hi, KB.....I was puzzled, too, like MrsB
Your dd sleeps so well, and this is at least part of the reason why she wants to feed a lot in the day.
Giving her a bottle of formula at night is not going to help her sleep any better or give you more rest.
If you are sure you want to give her a bottle (and it's not just to get that witch of an HV off your back!!) then fitting one in earlier would make more sense....but don't forget to factor in the work of getting the formula, preparing the bottle, washing and sterilising, making up the feed, before you're sure it will save time
Exclusive breastfeeding to 6 mths gives the best nutrition, but of course that's not the only factor to consider - it's up to you to weigh the pros and cons.
You need to think about the reactions of people around you, too. Do you think they might look all smug and say 'oh, good, kittenbaby has seen sense at last' (just judging from previous threads) and that might make you a bit .
Just a thought!