ref-timezones doesn't have any procs. It is just the data, but timezone_rules has the dates and offsets for all the known timezones.
You could load ref-timezones (or trim it down if you only need some of it) and easily calculate what offset is in effect from UTC/GMT. Then the user can just be presented with an option to their timezone, and never worry about offsets as the query will take care of it.
I hope I didn't misunderstand the problem. Also, there may be some procs in acs-datetime that can be used, I didn't write that package and haven't really looked at it.
