Not all Punto Mk1s are coded, mine isn't and it's August 1994. Look at your key carefully, if it's got a blue moulded plastic finger pad that has no obvious openings or splits in it then your car isn't coded and you can disconnect the battery for as long as you like. If it is coded you will probably get away with it, because the battery will already have been changed several times, and if it survived that it will survive any disconnect. Some cars will not survive any kind of battery disconnect without reviving them by inputting the PATS code afresh using some commercial device or other. Find out what you have first.