Code:
$ date +%s
1519398240
$ irb
irb(main):001:0> require 'date'
=> true
irb(main):002:0> Time.at(1519398240).to_datetime
=> #<DateTime: 2018-02-23T18:04:00+03:00 ((2458173j,54240s,0n),+10800s,2299161j)>
irb(main):003:0> Time.at(1519398240).to_time
=> 2018-02-23 18:04:00 +0300