action

# instead of Time.now (or watever class methods of Time), we use:
LocalTime.now

action

When %r{I press "([^"]*)" at "([^"]*)"$} do |button, timing|
  LocalTime.xstub(:now => LocalTime.parse(timing))
  When %|I press "#{button}"|
end

date_time.rb

class LocalTime
  @@zone = Time.zone
  class << self
    def method_missing(method, *args)
      args.empty? ? @@zone.send(method) : @@zone.send(method, *args)
    end
  end
end

environment.rb

Rails::Initializer.run do |config|

  # lots of other stuff

  # Set Time.zone default to the specified zone and make Active Record auto-convert to this zone.
  # Run "rake -D time" for a list of tasks for finding time zone names.
  config.time_zone = 'Singapore'

end