Had a quick issue with Rails 2.3.8 trying to get your plugin working (which is awesome by the way).
Rails was spitting out an error, "can't convert Array into String" and referenced:
simple_time_select/lib/simple_time_select.rb:52:in `select_minute'
To resolve this I changed:
build_select(:minute, minute_options) to build_select(:minute, minute_options.join(' '))
Hope this helps someone who wants to use this awesome plugin!