Ruby (the programming language) doesn’t have 10.hours, that’s ActiveSupport as part of Ruby on Rails (the web framework). And yes, it does have both minutes and seconds methods.
However, Time#+ (the + method on Time instances) returns a new Time instance that is that many seconds in the future. So without any Ruby on Rails sugar, you can simply do:
irb> t = Time.now
#=> 2011-08-03 22:35:01 -0600
irb> t2 = t + 10 # 10 Seconds
#=> 2011-08-03 22:35:11 -0600
irb> t3 = t + 10*60 # 10 minutes
#=> 2011-08-03 22:45:01 -0600
irb> t4 = t + 10*60*60 # 10 hours
#=> 2011-08-04 08:35:01 -0600