He's still just learning what it's like to be out in the big world so it's still very early days! Many babies at this age are still working out the difference between day and night, let alone sleeping for more than 3-4hours at a time. It sounds like he is doing very well to put in 6-7 hours in one go!

The only thing I can think of is to put him down at 4 but give him a top up feed at 8pm to see if he sleeps longer then. However, you run the risk of him waking. I always tried to have my babies awake from 4.30 - 7pm as this was Daddy time when he got home from work and was able to help bath and put them to bed. Then they had the long stretch of sleep from 7pm. They were about 2 months old when this really started working though. Until then I just let them go with whatever they wanted.