Hi D.,
my kids have always had an 8 pm bedtime. I have found though that at times when they stay up later than that, they don't sleep any later :)
My 10 and 12 yr old girls still have an 8 pm bedtime... and it's lights out,.. no exceptions. On the weekends, they still go to their room at 8 pm, and have to be 'in bed' - they can stay up talking or playing their DS's until 9 pm.
We do this mostly out of necessity now. My husband and I go to bed at 9 pm (I am up with the new baby by about 4:45 am and I stay up for the day at this point and he leaves the house by 5:45 for work). We need that hour at night to ourselves without kids.
One thing my first pediatrician told me (he was actually MY pediatrician when i was a baby...) is that kids truly need the sleep - they can function for the most part but you may see some negative behaviors and they may not do as well in school... etc. I dont know if that's the case as i have always had this bedtime, but I can say that when they stay up late (they do this at their dad's house on his weekends - they stay up til 10-11pm sometimes)they suffer for days afterwards... the night they come back from his place, they are wanting to go to bed at 7 pm.
I am willing to bet if you pushed the 2 yr olds bedtime to 8 pm, he probably wouldnt get up any earlier... of course you have to consider how long his nap is... if he's napping 3 hours, he may start cutting that a bit shorter with the new bedtime.
All in all i dont think his 830 bedtime is harming him in any way... 30 minutes in my opinion is pretty insignificant. And you have to consider what's best for your family - we're in bed early by mmost standards, so... it is all relative i guess :)