Calculate minutes played by players in sport

Please see the attached workbook.

sheet 1 is an event sheet.
column A are the dates of matches. there are 3 matches in total played on the 17th, 24th, and 30th Aug 2013.
in column B there is the player's number involved in the event.
column C is the event.
the words that need attention on column C are "Sub Off" and "Sub On".

I would like sheet 2, column C to calculate how many minutes the player in column B played on the date listed in column A.

remember the match lasts 80 minutes. thats the maximum a player could have played.
so if a player wasnt "sub off" then they obviously played 80 minutes.
if a player was "sub off" then they played for whatever column D says...
and the player that replaced them on "sub on" played for 80 minus whatever column D says .

hope that all makes sense

thanks

works fantastically. thank you so much...

however, there are two parts to my question. i didnt want to ask them both in the initial post because i thought it might put people off for being to complicated/difficult.

i was hoping for the formula to still work when a player is "sub on" and then is "sub off" later.
so if a player is "sub on" at 30 minutes and completes the game, they would have played 50 minutes.
BUT what if that player was "sub off" later at 70 minutes. The player would have only played 40 minutes (30mins to 70mins).

is it possible for the formula to calculate this?
its okay if there are any helper columns needed.

thank you