I recommend that any slideshow follows the meal and precedes the after-dinner traditions.
There are few reception traditions that kill a mood faster than a poor slideshow. Here are several pro tips you might consider if you're making your own slideshow.
Short Show: Limit your slideshows to 5 minutes or less. Longer shows don't hold reception guest interest. You don't want bored guests right?
Short Slide Duration: Most photos should appear for less than 1 second. Important photos should appear for no more than 3 seconds. For best results, I prefer that all photos be limited to no more than 1 second and most photos be limited to a half second. Short slide duration prevents viewers from getting bored.
One Song: Choose a universally recognizable and upbeat song with a duration shorter than 5 minutes. Your entire slideshow should run for the duration of that one song.
Simple Transitions: Avoid "fancy" transitions. Simply fading in and fading out between photographs is more effective than using varied distracting transitions offered in some slideshow software.
Variety Matters: Many reception guests won't know family members in your photographs. Intersperse fun and active photos of you and your spouse between static family photo groupings.
Equipment: Keep projectors and screens hidden. Don't set them up until immediately before your slideshow. Otherwise reception decor is negatively impacted.