How to Validate SIT using User Hooks

We created SIT and we would like to perfom a Validation on this SIT (Through Self Service) before Employee Submits for the Manager Approval, is this possible to perform?

I am using the user hooks CREATE_SIT

Please find below the code we are using but this code only fires after the final approval and we need it to fire before the Employe Submits For the Approval.

IS L_API_HOOK_CALL_ID NUMBER; L_OBJECT_VERSION_NUMBER NUMBER; L_API_HOOK_ID NUMBER;

NUMBER; L_OBJECT_VERSION_NUMBER NUMBER; L_API_HOOK_ID NUMBER;

NUMBER; L_API_HOOK_ID