When I saw the size of the time zones list I was about to quit.
To improve conversion and tries, I think you should :
1) Add a javascript filter to filter the list of time zone.
2) Automaticaly select the most apropriate using either language, IP geolocalisation etc... If it's not perfectly accurate, it won't be far.

Just seeing this awfull list made me wonder about the quality of the rest of your app.

I know it's just a one time setup, but it's about getting users, try a A/B compare on it.