I have just made a Pod parking booking and the confirmation email has the following text:

ENTRY
Drive up to the barrier. Your number plate will be read and a ticket showing your booking reference will be issued automatically. If not issued automatically, press the Help button for assistance. POD Parking operates between 04:30 and 23:00 between T5 and POD from POD Station A & B. Outside of hours an on-demand bus can be requested via 020 8745 6261.
EXIT
Return Transfer to POD Parking will pick up at Bus Stop 28 on the Terminal 5 Arrivals Forecourt. Cross to the 2nd lane and turn right. During off peak hours (23:00 - 04:30) please call 020 8745 6261 to request a transfer back to the car park. On return to the car park proceed to the exit, the registration will be recognised opening the barrier for exit. Press the Help button at exit for any additional assistance.

That reads to me like pod to the airport but bus from the airport, booking is for the end of march.