They say you remember the exact moment in time - what you were doing, who you were with and what day it was. When everything happened - Sana's world falling apart then bursting into an unknown oblivion - all that's needed to be remembered is that it's New Years' day and she was meant to spend it with Momo.

Time becomes but a loose concept, days are lost like grains of sand between her fingers, and if she wasn't befuddled enough - losing track of time is a game Momo plays like a fiddle. 

It's a race against time, mutiple times over again, and Sana wasn't meant to be playing.