Time Comparison and Calculation Questions

Question

Friends-
I work in an industry where my scheduled work time is limited by statute.  And I have to do calculations for work legality that are based by looking back at actual times and forward at scheduled times.  The "DURATION" format is amazing because I can enter 5H 47M and it appears as I require.  I can also easily add with SUM my required times.  But that is the easy part.
The hard part is it appears that while I can add and subtract DURATION formats, it is not a number, but a string.  (I think).  The problems I have are:
1.  I need to populate a column for calculations (Calc Column) which includes either my Scheduled Time or Actual Time.  I need to look backward on actual times (regardless of which is greater or less) and forward on scheduled times.  I put that value in the Calc Column and do running totals for 28 days at at time.
An IF statement would work perfectly here, if these were numbers, but unfortunately 0H 0M does not equal zero and I have been unable to make any If formula that states =IF(A1=0, X, X)   or   =IF(A1=0H 0M, X, X)   or   =IF(A1="0H 0M", X, X).    The only way I can test to see if a value is zero is with a string operator to look at 0H 0m and see zero's    =IF(MID(F44,4,1)+MID(F44,1,1)=0,E44,F44)
Can anyone think of a more elegant way to test for whether a column contains 0H 0M.
2.  I have to enter 0H 0M because I can't get any formulas to work on a blank cell.  I would much prefer to not see 0H 0M in the column and only see values on the days that I work.  But I have not been able to leave blank.  As you can see the only formula that works requires 0H 0M and not zero or empty.
3.  Conditional formating:  I have tried to conditional format so that any time the value of a cell exceeds 95 hours it turns red.  But formatting works on values, and not on my 0H 0M string.
Suggestions or solutions appreciated:

Answer 1

Ian:
Thanks, it almost worked perfectly, but not quite... 
DUR2HOURS solve the biggest problem that I had.  Unlike in you sheet I do not calculate on a start and ending time.  I start with a scheduled time for the day, then a computer provides me an actual time for the day.  So Column E is Scheduled, Column F is Actual.
DUR2HOURS allows the if statement you see below, namely to see if ACTUAL column is zero, it returns result of Scheduled.  Thank you, very nice solution and allows IF statement.
Small issue still left, I would like to leave the says that I do not work displaying blank.  Currently I have to enter 0H 0M every day or else the dreaded little red triangle below.  So if I could make a formula that did not return the triangle the spreadsheet would read nicer and I could move onto the lookup function that is also not working!
Thanks again for the excellent recommendation.
JG