zsh の history を元にして、開始と終了から時間を出します

calc_time.rb

require 'time'

wd = ["日", "月", "火", "水", "木", "金", "土"]

result = {}
while line = gets
  begin
    time = Time.parse(line)
    date = time.strftime '%Y-%m-%d'
    result[date] ||= []
    result[date].push time
  rescue
    nil
  end
end

result.each do |key, times|
  print "#{key}(#{wd[times.min.wday]})\t#{times.min.strftime('%H:%M')}\t#{times.max.strftime('%H:%M')}\n"
end