There has to be one in the operating company's Valve Specifications, otherwise it couldn't be commissioned properly and any fly-by-night could build and sell them with potentially disastrous consequences for the environment. So the first thing to check is the content of the operating company's standards book.

The second thing is the Control Philosophy document.

Thank you PWSlack. It is specified in the company's specification but I am looking for the basis of such requirement either 15sec, 30sec, 45sec or 1min is the correct and reasonable closing time.

The basis of the requirement has been considered by the individual(s) that authorised the specification for use. So this/these people, or their successors in similar roles, are the right one(s) to ask. If there is a concern over the content, then this is the correct arena for those concerns to be aired and the specification to be revised and reissued if necessary.

Thank you.

Yes, API standards!