(mongodb >=1.4.0)
MongoDB\Driver\Session::getOperationTime — Returns the operation time for this session
Returns the operation time for this session. If the session has not been used for any operation and MongoDB\Driver\Session::advanceOperationTime() has not been called, the operation time will be null
This function has no parameters.
Returns the operation time for this session, or null
if the session has no operation time.