Hi Edel,
I got a form when I was approved from my local SWO giving me the exact day it was collectable from the PO, in my case it was Wednesdays and it was always collectable on Wednesday's, I would recommend you find out your exact day either from your local SWO of by asking the staff at your PO if its on your claim on the screen as you only have a short period of time (I think 6 days) to collect your weekly payment before its deemed uncollected and you are deemed 'signed off'.