45 minutes would be an absolute maximum. I tend to bathe DS's before dinner because a bath hypes them up before bed.
Bedtime begins at 6pm. One of us takes a DC each. Whoever has DS(4) will do school reading from 6pm, then upstairs, brush teeth, in to PJ's, book of their choice and bed. He's usually in bed by 6:30.
DS(1) starts having cosy time, we might read a book before In The Night Garden begins at 6:20. He has milk from a sippy and when he's ready to go to bed he climbs off the sofa holding his muslin. Usually 6:30. I don't think he's ever actually finished an episode of In The Night Garden.
This totally changes at weekends though, but both DC are generally super relaxed about going to sleep.