Big jump in amount taken from expressed bottle - experiences?

[FenLondon]

My dd is now 5wks old, and for the past couple of weeks DH has been giving her the 11 o'clock feed from a bottle that I've expressed. She was steady at 2 to 3 oz, but for the past three nights has taken 5 or 6! She's weighing in at just over 4kg, so the amount's not unreasonable, but I'm more concerned that with winding, settling and preparing the second 3 oz of milk it's taking him 2 hours to do the feed, and he needs his sleep! Any advice? I know he's been reluctant to warm up the full 6oz as he doesn't want to waste expressed milk. My other concern is that if I can't "get" 6oz out in the day our options are he brings her in to me to top up (whole idea is I get some sleep and he bonds) or we use 50/50 breast and formula. I can generally get 3oz expressed at 10:30 pm, and the rest comes from what I've got during the day.
Ideas on keeping the feed time down, and experience of introducing a little bit of formula? I'm obviously keen to keep her on breast milk as much as possible but I don't have a problem with a little bit of formula if we acheive a good feed for Dad, a good sleep for Mum and a good feed for Baby.

There's a 6 week growth spurt so your probably coming up on that. During a growth spurt it's probably better that you do do the feeds because you have the best supply at night and missing those feeds could have an impact on your supply. After six weeks you will probably find that you start settling into a routine better than you have before anyway and start getting more opportunity to sleep.

There are plenty of things that dads can do to bond, bottle feeding doesn't compare to breastfeeding for the bond and I've never found it any different to anything else I've done for a child.

My ds is 7mo and hungry! and I breastfeed. We got round the bonding issue with dh by making bathtime dh's special job - I do the feeds and he does the baths and this has worked well for us as he still gets skin to skin and 1-1 contact. I think I have only bathed ds about 3 times when dh has been away on business. He now occasionally give ds a bottle of expressed milk if I am out.

Thanks everyone. This is the only feed that's gone up (all the ones through the day are very consistent with the past couple of weeks, yes I'm a* retentive enough to track them ), which is why I hadn't immediately thought - "aha - growth spurt", but that's a very good point re supply TinkerBellesMum.

"Problem" with bfing is you have no idea how much is taken at each feed so it's quite possible that the other feeds have gone up without you knowing and as I said before, night time is when mum has the best milk so baby will increase that one first.