New to Excel .. Formula for a time related issue

1) I am trying to check the differences in 2 times in 2 different boxes for example the time in d5 is 23:30 and in c4 is 17:00 the previous day i need to right a sum that without the answer being visible does something like turns the square red if there is an error. I need to ensure that there is atleast 11 hours between and 2 times it can be the same day or a different day i would word it similar to this:-
Check that difference between D5 and E4 is equal to or more than 11 hours if it is not then tun d5 red a visual warning that There is a problem.
That is the first thing....
2) i want o count and show by turning a square blue that if the difference between d5 and d6 is greater or equal to 10 hrs if so turn d6 blue and if possible ad 1 to a counter counter can be in z1 for example.


********* I HAVE ATTACHED A REAL LAYOUT EXAMPLE AS WELL **********


If anyone can help with either or both i would be greatful..
I have heard you have to out this action somewhere else in excel so a bit of an idiots guide would be good thanks again
posted in programming as well thank you