hsh.rb

hsh = {}
ary = ['02:40', '04:20']


first, last = [ary.first.split(":").map(&:to_i), ary.last.split(":").map(&:to_i)]

hsh = {
  first[0] => (60 - first[1])*60,
  last[0] => (60-last[1])*60
}

((first[0]+1)...(last[0])).each { |n| hsh[n] = 3600 }

puts hsh #=> {2=>1200, 3=>3600, 4=>2400}