I've spoken to the depot three times today (two separate guys). I was brave/foolish enough to mention that I'd heard they weren't allowed to hold the package before a delivery attempt was made. They both went and checked with managers and confirmed that it would be fine to pick up the package tomorrow at 8am. They both mentioned that if I check the tracking details it will now show as delivery on 27th. Apparently they do this as standard procedure so that when the driver arrives for work tomorrow morning and scans the packages on to his van he'll get a message telling him to leave my shipment behind at the depot. Was told this by both guys I spoke to.
In the past I've found that their tracking system updates very early in the morning (between 5-6am) stating that the package is out for delivery. So i guess we can check prior to making the journey to the depot.
Good luck!