I use this code (for easy migration from PHP4 to PHP5):
/**
* Constant definitions that has been removed from PHP 5
*/
const IBASE_DATE = "ibase.dateformat";
const IBASE_TIME = "ibase.timeformat";
const IBASE_TIMESTAMP = "ibase.timestampformat";
/**
* Sets the format of timestamp, date or time type
* columns returned from queries
*/
function ibase_timefmt($format, $where = IBASE_TIMESTAMP)
{
ini_set($where, $format);
}