For a more modern slant, I always thought this would be a beautiful song for first dance . . .
Listen to the words.
But it is long and I agree with other posters that you should keep your first dance on the short side unless you bring in other people to join you on the dance floor.
I think 2-3 minutes is perfectly fine for a first dance. 30 seconds? In my opinion, is way too short.
I've seen it where the B&G start the dance, then they visibly invite the parents of the B&G on the dance floor for a minute or so, then they invite the bridal party to the floor to finish the song/dance. I thought that was really nice because it showed that the couple isn't in this marriage alone, they have family and friends to surround/support them.