I would be careful about getting too excited about changing the delivery date or collecting from dpd before Tuesday as I did the same for today and it didn't arrive. Was supposed to be delivered between 8.30-10:30. My guess is that DPD's website is poorly designed and allows you to collect and change delivery dates even though they haven't collected the parcel from CPW. I doubt carphone warehouse will release the parcel till Monday for delivery on Tuesday.
If you use the tracking details on the DPD website and click on additional information. The collection date will be blank which means it hasn't left carphone warehouse
Just warning you guys so you don't waste a journey or stay in waiting for a parcel that won't come