The date fields are formatted as dd-mmm-yyyy; the time fields are formatted as HH:MM
OK, then you can use this code as the custom calculation script of "Expiration Date":
var packedDateString = this.getField("Packed Date").valueAsString;
var packedTimeString = this.getField("Packed Time").valueAsString;
if (packedDateString=="" || packedTimeString=="") {
event.value = "";
this.getField("Expiration Time").value = "";
} else {
var expDate = util.scand("dd-mm-yyyy HH:MM", packedDateString + " " + packedTimeString);
expDate.setTime(expDate.getTime()+(60*3600000));
event.value = util.printd("dd-mm-yyyy", expDate);
this.getField("Expiration Time").value = util.printd("HH:MM", expDate);
}