It's been a while and I'd forgotten what a pain in the ass tracking down the documentation is, but I think this will work. I move to LibreOffice a while ago though, so you might want to test it on a small selection before running it over 5000 rows of spreadsheet. Included comments to explain what I think I'm doing.
Dim var As Range 'variable var is a dimension defined as the range; rename "var" to whatever you want if you care to
Set var = Range("B:B").Find("Duration: ") 'range is set to column B (assuming B is the duration column from your example, change to the appropriate column if this is wrong)
Do While Not var Is Nothing 'loop should execute until B is empty (the end of the data)
var.Insert xlShiftToRight 'data is shifted to the right
Set var = Range("B:B").FindNext 'move to the next cell in the range
Loop 'close loop
Should work in 2010