Hope it works out,
Just be there early, so the postman doesn't leave with it.
If you explain the problem, they can at times be helpful.
Most of the time I have gone down there, as it is a problem sometimes to ring....they don't answer the phone.
Most of the bigger PO have a bussiness door or counter somewhere, so bussinesses can pick up their stuff early for the new day.
Again good luck and I hope the sky's clear for you as well
John