Wake window is the total amount of time that your baby stays awake between two napping periods.
Wake windows ensure that a baby stays awake for long enough to fall back to sleep immediately.
However, the baby must not get over exhausted. That might just increase adrenaline levels in their body which won’t allow them to fall back to sleep.
If your baby is also being fussy about sleeping, maybe they are not spending enough time awake to fall back to sleep again.