I don't think you need more than a minute even but that depends on how long you have to walk down the aisle I guess...
I discovered the "Vitamin String Quartet" and LOVE their music. They interpret a ton of classic heavy & alternate rock and pop songs from artists like Queen, Michael Jackson, AC/DC, Guns & Roses, The Beatles, Madonna, Kiss, etc.
I chose "The Power of Love" by Celine Dion. Played in string quartet, I find it's a very classy and touching piece.
I'd like to play other songs from them during cocktail hour like "I was made for loving you" by KISS. It's pretty funny to hear such a classic rock song played by violins. They are VERY good!