Postgres error "invalid value for parameter "TimeZone": "UTC""
I had the same problem using the Postgres.app from Heroku. Rebooting my Mac solved it.
Restarting postgresql works.
To restart if you've installed it using homebrew, brew info postgresql will tell you to:
launchctl unload ~/Library/LaunchAgents/homebrew.mxcl.postgresql.plistlaunchctl load ~/Library/LaunchAgents/homebrew.mxcl.postgresql.plist