Not much different...
time_now = Time.now time_one_week_from_now = time_now + 60 * 60 * 24 * 7
http://www.rubycentral.com/book/ref_c_time.html
There's some other date helpers in rails that may be useful too http://rubyonrails.com/rails/classes/ActionView/Helpers/DateHelper.html