From DX FAQ:
"Live tracking is only available after the carriers have a chance to initially scan the package. Between the time the item leaves DX and the time it is scanned, tracking numbers may not show any results. For Express packages (sent via EMS/UPS), the delay is about 24 to 48 hours. For Airmail and Registered Airmail packages, it takes 3 to 5 working days for postal tracking to show online."
GX255, if it asks for your Enquiry Reference Number, I'm pretty sure your package hasn't been scanned yet. Once it's been scanned, (and assuming you've clicked on the tracking number fom DX), you won't need to be inputting any numbers, the status of your package should immediately show up.
From my experience anyway.