We're where you are at with DP's son atm - albeit he's nearly 6 but he essentially has "two" bedrooms to sleep in. His mother always lets him sleep in with her if he kicks up (70% of the time) so it's a ballache trying to educate him that he has his own bed, which he has to sleep in - we don't mind him coming into ours if he's poorly or had a particularly bad nightmare, but we don't tell him that - we just offer it to him at our discretion.
Anyway - it's a tough one. DSS isn't really insolent as such, he just HATES going to bed; he feels like he is missing out if he's upstairs and we're down here (couldn't be further from the truth, we're so knackered we usually veg out). We have a tactic that one of us will put the bed, and once that person has said goodnight, it is only that person who responds to any (inevitable) calling out.
DSS works on a 3 strike system although he isn't aware of it. He gets one call out which is responded to either by bringing him what he needs (drink, turning light off/on) or answering a question. He has five minutes to use it and then whoever is doing bedtime goes downstairs. 2nd call out is answered from the bottom of the stairs, so no going up, no getting into conversation, just a firm "bedtime, love you, night night" (usually proceeded by further calling out, which often dies down after we say "bedtime, please"). 3rd call out is ignored, unless we can hear distress, illness or issues - again, he isn't aware of what constitutes this - his Mother, bless her heart, says "If you feel ill tell me" (she's very, very overprotective cotton-wool, which is her way and none of my business) so he nearly always will say "I've got a headache" - cue calpol, cue him getting into her bed. Usually, after the third call out, he'll recognise we're not coming up and will either fall asleep or play with lego/read a book, and is asleep within quarter of an hour.
It really does depend on his mood, I'm afraid - we've had 10pm screaming fits where he's thrown every trick at the book at us, and we've had occasions where he's taken himself up to bed at half 7 on his own volition (bliss 
) - it depends on the week he's had at his Mum's, how often she lets him sleep in her bed and how much activity he has done - we've seen that if we wear him out, eliminate most forms of sweets after 5pm and read to him or play something calming with a drink of milk, he's ready by about half 7. It's 8:45pm at the moment and he is still awake, but one of the drawbacks of having a blended family where we only see DSS at the weekend (we wish it was more) is that he often feels angry at the idea of going to sleep - he just wants to spend more time with us, which is obviously often how we feel too so small allowances are made - tonight, simply because there is only a few days of school left.
We also found out there were certain things in his room he didn't like placed in certain ways - like teddies facing the bed or toys on the windowsill as they cast a shadow - stuff we wouldn't think about necessarily. May be worth, if you haven't already, just to idly drop into conversation (ie not during bedtime rountine, otherwise every single thing in his room will be an issue and he'll milk it!) in the morning whether he'd prefer something moved around in his room, or whether something is bothering him about when he sleeps. We found out DSS was having chronic nightmares about three months ago because he was watching a couple of YouTube videos that although were innocent enough, for some reason sprung a nightmare in his head - now we completely shut down YouTube after dinner, and he is only allowed to watch videos when we are present in the room - not sure if his mother is doing this, but imagine she is too as nightmares have lessened. Sometimes the really simple things fuel their imagination!
Hope some of that helps - I also recommend the two books mentioned here.