Mass update with Date Field Formula

I'm trying to update a custom Date field in a Transaction record via a Mass Update formula.

This update looks at the creation time of the transaction, and creates a billing date based upon the time the order was placed.

CASE WHEN (to_char({datecreated},'HH24') < ’12') THEN (to_char({datecreated}+5, 'DD-Mon-YYYY’)) WHEN (to_char({datecreated},'HH24') > '11') AND (to_char({datecreated},'HH24') < '18') THEN (to_char({datecreated}+7, 'DD-Mon-YYYY’)) WHEN (to_char({datecreated},'HH24') > ’18') THEN (to_char({datecreated}+7, 'DD-Mon-YYYY’)) END

In this example, if the order was placed before noon, the billing date is 5 days away, if it's between noon and 6pm or after 6pm the billing date is 7 days away.