Non-overlapping windows

A courier's assigned delivery windows for one day are given as [start, end] pairs in minutes; the courier is occupied for the half-open span [start, end). The list is unsorted. Return True if a single courier can work all of them, i.e. no two windows overlap. Back-to-back windows, where one ends exactly as the next begins, are fine. Example: [[30,75],[0,30],[75,90]] is True.