I've made the analogy before here, but...
Think of RSVP as a carnival game where you have to get a ball in a cup. The cup starts at your feet and moves away from you. The track that it's on is marked off in 5 second increments. As the cup is moving away, a 5 second section lights up. You can only win the game if you get the ball in the cup inside that lit up section.
So let's translate that to the RSVP... NikeATL sends out the hashtag picture. You respond within 1 second... you sent it when that timeframe wasn't what Nike picked, though... so that doesn't count. So, you send another DM... again, the timeframe wasn't correct. Again, you send another DM (let's say 25 seconds after their initial tweet)... congratulations! You sent your DM in the timeframe that Nike picked to accept DMs.