Does Agile move too fast for Usability?

Agile's defining characteristic is speed. Unlike other software development methodologies (like Waterfall) that work in timeframes of months, Agile timelines are measured in weeks (2-4 typically) with actual code developed for each 'sprint'.

Is Agile's rapid and fixed development deadlines and deliverables conducive of usability activities? In short do you have time to do usability?