I suspect that there is more to the story. Obviously you aren't extending one line..
So... how big is the featureclass? does it reside on a network?? Do you have permissions to modify the features?
Are your data projected or does it have to do a reprojection to get 23 meters all the time? Have you tried a subsample of say 10 lines? How long did that take?
Turns out the tool was not doing what I thought it was. I thought it would extend by 23 meters when that value was provided. Not that it would extend to a maximum of 23 meters. I need a tool which will extend all lines by 23 meters.