I also called IND and they confirmed what joebloggs is saying. There is a 28 day allowance, but beyond that, you must apply for FLR so it seems, BUT do call them and see if theres some way leeway.
On another note, I'm doing battle with the BE Embassy Manila for the return of the documents submitted during Elsa's application over 2 years ago, they still haven't returned them (these documents are all my bank statements, birth certificates, etc). I was told I could have them back after 2 years, but how come you lot are getting all your documents back with the visa being issued? A visit to a solicitor might be on the cards if I don't get them back soon, I'm not a happy bunny.