Because of the invasion that happened during the night, with the shinkansen being derailed and all, the city government decided to just call the next day another day off since there were considerable damage to a portion of the city.
And since Murasaki Saki wasn't able to get on the train before the accident occurred, she had to stay another day in Tokyo. Fortuantely, they were a whole ten minutes late before everything came down, otherwise, she'd have been on the train and it would've been a disaster.
For some, this setback would've been enough to be a disappointment but for Saki, she deemed it as divine intervention. Since she was not the realist type, she assumed that this was the work of something up above so she could get closer to Midori.