class Date

def to_time(form = :local)

date.to_time(:utc) # => Sat Nov 10 00:00:00 UTC 2007

date.to_time(:local) # => Sat Nov 10 00:00:00 0800 2007
date.to_time # => Sat Nov 10 00:00:00 0800 2007

date = Date.new(2007, 11, 10) # => Sat, 10 Nov 2007

The timezone can be either :local or :utc (default :local).
Converts a Date instance to a Time, where the time is set to the beginning of the day. 
def to_time(form = :local)
  ::Time.send(form, year, month, day)
end