def assure_time arg=nil, opts={}
      if arg
        arg.kind_of?(Time) ? arg : Time.gm(*arg.split('-'))
      elsif opts[:default]
        Time.send(opts[:default])
      end
    end
def assure_time arg=nil, opts={}
      if arg
        arg.kind_of?(Time) ? arg : Time.gm(*arg.split('-'))
      elsif opts[:default]
        Time.send(opts[:default])
      end
    end
A helper function to assure a value is an instance of time
 @param [Time, String, NilClass] arg The value to be asserted
 @param [Hash] opts Options for assertion
 @option opts [Symbol] :default a method that can be sent to Time if the argument is nil (:now for example)