Calculating difference based on specific cell values

I need help making a macro that will calculate the difference between two activities based on the following activity. I have attached a sample workbook.

So, I want to be able to calculate the time difference between cells from column G when the New Status is "complete" and the one underneath it is either "Available, transit, up". I know the last two aren't on the spreadsheet, but they are in the master sheet.

I wouldl like to calculate the time difference when there is a change in Column I from the "Complete" status to "Available, transit, up". The last two aren't in this spreadsheet, but they are in my master spreadsheet.

So one example would be that in row 22 in column "J" you would have a value of 23:00:21, since the status changes from "Complete" to Available (the bottom status).

There would also have been a value in row 15, but it is a negative so I don't want anything to show up.

So you would be subtracting cells G23-G22, since I would like to measure the time it takes to go from "Complete" to "Available" in column I.