The invitation specified the wedding and the dance. Yes, the wedding was in the afternoon and the dance was at about 8:00 at night. My boyfriend at the time had commitments during the day, as did I, so we made plans to go to just the dance, especially since there was that several-hour gap in between and the two parts of the event were in different cities (neither of which was where I lived). I think there was probably a separate enclosure card with the specifics of the dinner, if you were invited. I didn't get one of those.
I *thought* we were close enough friends where I would have been invited to everything, so when there was no dinner invitation, I guess I just thought they weren't having one or were having a very private family-only dinner. (And nobody would start a dance before 8 p.m., so I figured they just did their own thing until it was a 'proper' time to start a dance.)
The uncomfortable part was arriving there and finding that the party was in full swing....that is, the reception/dinner part of the party. They hadn't started the dance yet, which meant that yes, the lights were on, the tables were still set up, and people were still milling around after eating. Since the dance hadn't started, I felt like we were crashing the party, because it was obvious that even though we arrived at about the time we were invited, the celebration had already been going on for a while. Add to that some level of embarrassment from me, when I (somewhat) dragged my boyfriend to this friend's wedding and then was kind of slapped in the face that we didn't get invited to the dinner. I felt kind of B-listy and out of place; embarrassed that 'oh, guess I'm not such a good friend after all. Huh.'. Maybe if I'd noticed a bunch of other people coming in at the same time as us (fellow dance-only invitees), then it would have been better, but it appeared that I was the only one. Sure, people said 'hi', but they were already in groups by then. Just try to imagine arriving at a party at the time you were invited, to find out that it had been going on for a few hours already. It was just....uncomfortable.