Inflated setup time of operations

Hi Experts

We are facing an issue where setup time of an operation is inflated to a very large number after the order is converted from APO. For example if we have std value for set up time maintained as 15 mins for op 0030, after conversion the set up time of op 0030 shows a very large random number such as 4,500 mins. I am unable to get to the root cause of the problem. Please advice . Thank you