in the zone

gistfile1.rb

# default zone
Time.zone # => (GMT+00:00) UTC

# then we can assign zone like use "Hawaii"
Time.zone = "Hawaii" # => "Hawaii"

# then do local using zone
local = Time.zone.local(2012, 8, 1, 15, 30, 45) # => Wed, 01 Aug 2012 15:30:45 HST -10:00

# then save this local to a column and save
# (it will be converted auto to UTC by rails when save in table)
# take note our Time.zone is still "Hawaii" so
activity = Activity.first
activity.update_attribute :created_at, Time.zone.local(2007, 2, 1, 15, 30, 45)

# and when
activity.created_at # => Wed, 01 Aug 2007 15:30:45 HST -10:00

# now change back Time.zone to UTC
Time.zone = 'UTC'

# and do
activity.created_at # => Thu, 02 Aug 2007 01:30:45 UTC +00:00