How to introduce a bedtime routine?

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Hi

DS2 is 6 weeks old and is a happy and contented baby most of the time.
He wakes twice a night which is a dream compared to DS1! So I've not been too bothered about much of a 'routine' however he doesn't go to sleep until 10:30pm he wakes about 6pm and stays awake until this time.

DS1 goes to bed at 6:30 pm and is up at 7am for school when DS2 would still sleep. So although DS2 has got himself into his own little routine by himself which is fab, it doesn't slot in with DS1s at all which means I am constantly on the go from 7am until 10:30pm waking twice and having no time for a bath or to watch a programme with DP so this week we are really starting to feel it a bit as there isn't a moment of 'child-free' time at all.

Can I even introduce a bed time routine at this age? If I can how do I even go about it if DS2 wakes at 6pm to stay up for the evening. Has anyone managed to implement a routine or an earlier bed time? Even 9pm would be a great improvement for an hour to have a bath or a bit of time with DP.