I did a search and wanted to add more to this thread...sorry for bumping it up, but it could be helpful to others who search too.
"Or if you're comfortable tweaking the source code, look for the array called $show, as that's what's used to set visibility: e.g. $show['dateCompleted'] sets the visibility of the "Date Completed" column."
For reference, edit displayItems.inc.php and add at the top:
<?php
unset($show['timeframe']); //Hide the Time Context Column
unset($show['recurdesc']); //Hide the Repeat Column
?>
Ajax addon will allow you to unhide these.