I have a single order consisting of two items, one shipped with DPD and one GWUI,
The GWUI item was dispatched two days after the DPD item, but arrived yesterday and updates from the Amazon App were on time. Overall the item was 5 days earlier than expected.
The DPD parcel said it was out for delivery 3 days ago and still hasn't arrived as yet.
So over all it can be a bit random.