While all the lines before these are basically about sex, these lines show a deeper meaning to the song.
Remember how most people believed the world was going to end in December, 2012? And remember how it... you know... didn't? And remember the record-breaking birth rate about nine months later?
If you only had four minutes left to live, there's no time to be "hesitating" about what you want to do. And who cares who you do it with? Just "grab" someone.