6 month old early bedtime

My baby is 6 months old. She currently sleeps 5/5.30pm to around 3/4am, i'll give her a bottle & she usually falls back asleep until around 5/5.30 & from then on she'll just sleep for 20 mins then want her dummy etc until 6.30 when I get her out of bed. It sounds ok however, I hate her going to bed so early. My partner works until 6 some days so doesn't get to see her plus I can't take her out because I have to be back for her bedtime, when all my family work full time it's crap as they don't get to see her.I've tried letting her have a nap at 4/4.30 until 4.45/5 and then put her down at 6.30/7 however she is just super cranky, she'll cry & rub her eyes the whole time she's awake. Then once she's finally asleep they'll wake up so many more times than she usually does i.e every hour from 10/11 and then wakes up crying at 5/5.30 (whereas now she wakes up happy).Has anyone else had this?What can I do?I need to get her to go to bed later, especially since I'll be going back to work in a few months.Btw this has been going on for about 15 weeks so it definately isn't a growth spurt or a leap or a regression etc.Thanks, x