@Bwana Lawi - Just to throw a spanner into the works - is it guaranteed that the task will be completed within 24hrs? or does the system reset every 24 hours?
 
Anyway, if the start time is less than end time (meaning they fall on same day) I can do a direct compare. 

 
What if the task starts today at 8am and ends tomorrow at 9am - then the above assumption wont work.