Excel: How to force cell evaluation

Yes, it bugs me too.

dim c as range
for each c in application.intersect(activesheet.usedrange, activesheet.columns("C"))
  c.value = c.value
next

If all your cells have some text in common, you can also do a find/replace - in your case find every ":", and replace it with a ":" (i.e. find a way to find/replace that does nothing), and excel will re-format the cell.