I think, if I've understood this, add a column to give a 1 or 0 dependent on whether 4 visits have been made. Then I'd have another column saying if 4 visits column contains a 1 then calculate the difference in time. I'd then average that.
@Chalfie started
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I think, if I've understood this, add a column to give a 1 or 0 dependent on whether 4 visits have been made. Then I'd have another column saying if 4 visits column contains a 1 then calculate the difference in time.
I'd then average that.