I needs to convert a string into date and push that json into account expiry in AD

am pushing the string date as : customproperty39 = 20240210
and i needs to convert into date and needs to push into account expiry.
currently am trying like below but not working :

“accountExpires”: “${if((user.employeeType.equals(‘Contractor’))&(user?.customproperty39!=null)){10000*(user?.customproperty39.getTime()+11644473600000+18400000)} else {‘0’}}”