Bedtime help for 4 month old

[RunnerMummy18]

I'm a new mum to my 4 month old DS and I'm so confused about bedtime, we have no set time.

At the moment, he falls asleep on me downstairs around 8pm and then I put him to bed (next to me cot) at 10pm with a bottle. Sometimes he will wake up at 3am for milk and then sleep until 7/8ish, sometimes wakes up for his dummy every hour!

My mum friends all have 7pm bedtimes but our naps are so unpredictable still in length during the day. Today he really wanted to sleep again at 5.30 despite waking from a 2.5 hour pram nap at 4.

Help! Should he have a bedtime?!

My 4 month old (nearly 5 months) is the same as yours.
He's usually up around 7am, never know when he'll nap during the day, when he does its only cat naps but he usually falls asleep around 8/8.30pm. I keep him with me in the living room till I go to bed as the other half works nights & gets up around 11pm so I keep him with me so we don't disturb him too much. He always stays asleep when I move him into his cot & sometimes wakes for milk around 3am but not often although his dummy falls out every half an hour from around 4am 🤦‍♀️