How long is a bit of string ? If your IP gets the RX4 out right away it should only take a couple of weeks or so, depending on the size of the in-tray pile at Land Registry. From dealings with LR in the past, they are not the fastest kids on the block though.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014