Formula required to add time at rest
I have solve the above formula requirement.
I posted this on discussions.apple.com. Link to discussion is https://discussions.apple.com/thread/7778822

I had to add a hidden column H:H, then the formula 


  =IF(F3=DURATION(,,24,0,,),F3+H3,DURATION(,,0,0,,))
  +IF(F3&lt; DURATION(,,24,0,,),F3,DURATION(,,0,0,,))


I then copied formula all the way down column H



The second formula in I:I column is written so that it only returns a time if there is a time in the B:B range.


  =IF(B2="","",B2+H2)




I hope this helps someone. It has really made my life easier.