timer.rb

#!/usr/bin/env ruby

def say(str)
    system 'say ' + str
end

presentationTime = 300
discussionTime = 60

say '3'
sleep 1
say '2'
sleep 1
say '1'
sleep 1
say 'スタート'
sleep [0, presentationTime - 60].max
say 'あと1分です'
sleep 60
say '発表終了です'
say '質疑応答開始です'
sleep discussionTime
say '終了です'