[REMEMBER THIS IS ALL FICTION]
During Part 2 of the Season 5 Finale, Twilight Sparkle reenters the past the confront Starlight Glimmer once more after escaping from a changeling-infested future. Twilight then proceeds to try to beat Starlight in a magic battle.
What viewers witnessed were roughly 45 seconds of action that ended with Twilight and Starlight landing back on a cloud, exhausted and out of breath, before hearing an excited cry from filly Rainbow Dash and the other two colts who were watching in excitement, having been distracted from the race.
However, things don't add up at all here. After fighting Tirek in the Season 4 Finale for about the same amount of time and quadruple the magic power, neither were exhausted in any way. Because of this, there should be no way that Starlight and Twilight, two of the most powerful ponies in Equestria, can run out of power in less than a minute. Also, how could all the other fillies be acting excited over watching less than a minute of action?T he answer is simple. They fought for almost an hour, but (thanks to Sweetie Belle's reminder of friendship problems being over in half an hour or so) it had to be shortened to fit the air time. The full fight is available to all to watch....I mean, read...
Note: Twilight and Starlight are really the dominant characters in this...