I've answered this in Yahoo Answers and here is my answer to this question:

Answer:
Usually a cocktail/hors d'oeuvres reception last for 2-3 hours. Here is a simplified timeline:

First half hour
1. Drinks and hors d'oeuvres passed around on trays
(This may be the time that you are still taking photos)
2. Light cocktail music

Second half hour -
(Bride and Groom enter)
1. Introductions and toasts.
2. First Dance
3. Have person with mic mention that there are hors d'oeuvres stationed on a table and welcome everyone to dance.
4. More drinking, eating and dancing.

Second hour -
1. Cake cutting
2. More dancing, eating and drinking
3. Thank everyone for coming and mention you will have more drinks, hors d'oeuvres and dancing for the next X minutes.