>
> > for date formating 'dd-mm-yy hh'

Miss interpretation is very likely in your two digit format with dashes as separator!!

I would recommend to cast the timestamp to a char(24), resulting in a well defined ISO-8601 date time string (en.wikipedia.org/wiki/ISO_8601).

example for ISQL in firebird 2.5:
select cast( cast( 'now' as timestamp ) as char(24) ) from rdb$database

Good luck
Christian