conditional formatting to change colour of cell based on formula result

HI

new here so please be patient

I am not a master of excel but have been asked to perform a task in this application. I am wanting to make 4 columns .

col A is a time (say 12:00) col B is a time that will always be after col A (say 12:10) thats the basics
column C will be either an "I" or an "S".

If col C is an "I" then column D should be the value of B - A. If this results in a value over 00:12 (12 mins) then it need to be depicted in Red if under 12 then it should be Green.

If Col C is an "S" then the 12 min threshold changes to an hour. but with the same outcome. Ie if Col A is 12:00 and col B is 13:01 then col D is B - A. (the result being 61 mins which is over the one hour threshold thus should be displayed in red if under in Green.

I see col C being a drop down box but thats as far as i get. the formula eludes me and some pointers might "open my mind... Quade" sorry to question this on a saturday night.

thanks for constructive comments in advance.
Gideon

Can't you just use conditional formatting with column D simply being (B - A)
Something like

OR(AND(C1="I"),(D1<TIMEVALUE("00:12"),AND(C1="S"),(D1>TIMEVALUE("01:00))
set colour to red else green

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