Copy previous row value including IF statement

I’m guessing that the Start movement and End Movement Data is auto populated. Hi about this?

1. Add a custom column concatenating start movement and end movement i to 1 column. 

2. Remove any row in the new column that is Nul

3. Delete column created in 1 

this should leave just rows t have a time stamp. 

Then fill the end movement column up. You may need to fill tblank cells with null first, depending on your data 

then you should have all the start movements with the same end movement time.  

Add a difference in time column. The longest (max) value for each end movement must be the correct row. 

Hope it makes sense. I would need sample data to do this properly - this is just a best guess.