The formatting can be done like this (I assumed you meant HH:MM instead of HH:SS, but it's easy to change):
Time.now.strftime("%d/%m/%Y %H:%M")
#=> "14/09/2011 14:09"
Updated for the shifting:
d = DateTime.now
d.strftime("%d/%m/%Y %H:%M")
#=> "11/06/2017 18:11"
d.next_month.strftime("%d/%m/%Y %H:%M")
#=> "11/07/2017 18:11"
You need to require 'date'
for this btw.