G-ABCD: "MadeUp Radar - G-ABCD.."
MadeUp Radar "G-ABCD.. pass your message"
G-ABCD: "G-ABCD request FIS"
MadeUp Radar "Pass your details"
Dave, you've got the scenario wrong. The "pass your message" is an invitation to tell your life story, or at the very least your details AND your request. Ideally, your message contains everything the controller needs to know. So there is no further request for any details.
But if you're going to feed the controller your details and your request in little bits, yes, then it's going to take much, much longer.
BTW is "pass your details" actually CAP-whatever compliant? I only know about "pass your message". In any case it's a UK thing and I don't fly there all that often. The rest of the world just uses "go ahead" or something when the controller is ready for your (possibly lengthy) details and request.