Nearly 3 months, because the official paperwork got lost, then left in people's in-trays. I didn't chase it up at first as was feeling unusually considerate of the administrator's workload, though I ended up wishing I had as the whole business got dragged out for months. You could ask the staff responsible for getting yours sent out, to see what official stuff needs to happen before you get the paperwork. It's Easter soon and people go away on holiday and departments close for a while, so that's a good enough reason to ask!