AfterSave event in custom add

I have a custom add for an add page.

In the custom add I either return true to add the actual record, or I update a record and return false so it doesn't try adding the record.

I have this code in the JS Onload event.

It doesn't work, which probably makes sense since I'm not adding a record the normal way.

What I want is instead of the Record was Added, Back to list, I would like the Check In/Out was completed message to pop up in both cases.

Thanks
Alan