Watch 5:15 to 7:15
When thinking of decisions that could be made the idea of taking the lift or the stairs, or in fact the time you take it all stemmed from this scene I saw a long time back in "Harold & Kumar Get The Munchies".
The only difference is that in this scene Harold is daydreaming rather than it being on 2 separate occasions. I like this idea that the fact you say some thing when you usually wouldn't could not only affect your life but also the person you were speaking to which could have a knock on effect creating a huge chain of events. This could be the one change that has made the change in the sequence. From here I need to look into other possible changes that could be made to see if there is a better one I could use that would be more obvious for the audience to work out in the time scale.