Calculated Column slows view 3 fold

I start with an Attribute view, and then  build  a CV ontop of that.

If I simply add columns directly to output of the CV, the data preview takes 1.9 seconds.

I now add a single calculated column : date("AEDAT_CreatedOn")

My data preview now takes 6.3 seconds !

(total rows in data set 2.5million)

To me, that seems a hit on performance in excess of what I was expecting.

Can anyone comment on whether they think likewise ?

Any alternative way to achieve my conversion from string to date ?

Many Thanks