When my 2.5yo was dropping her nap, I would put her down at 6pm & she would fall asleep within a few minutes & would wake at 6am the next day. I have personally never had a problem with her not making up for sleep at night... she's always done 12hrs (or very close to).. but if I do later bedtime she would still only wake at 6am & we'd have a brief night waking as well.
On the day she would nap she would only sleep 1hr or so.... I would suggest cutting the nap to 1.5hrs which might help him fall asleep sooner than 8.30pm & he might sleep 10.5hrs at night instead.
Personally on the days he doesn't nap I would aim for bedtime earlier than 6.30pm. We used to do dinner by 4ishpm, milk & then snack around 5.30pm, potty & books so that she was in her cot & I was out of her room by 6pm.
hth
Layla