Time

1.day #=> 86400
2.days #=> 172800

Time.now.to_i #=> 1334222062

Time.at(1334222062) #=> 2012-04-12 18:14:22 +0900
Time.at(1334222062) + 1.day #=> 2012-04-13 18:14:22 +0900

Time.at(1334222062).to_s(:db) #=> "2012-04-12 18:14:22"

Time::DATE_FORMATS[:date_ordinal] = lambda { |time| time.strftime("%b #{time.day.ordinalize} %Y") }
Time.at(1334222062).to_s(:date_ordinal) #=> "Apr 12th 2012"

Time.local(2012, 4, 12)   #=> 2012-04-12 00:00:00 +0900

Time.now.beginning_of_day #=> 2012-04-12 00:00:00 +0900
Time.now.end_of_day       #=> 2012-04-12 23:59:59 +0900