Life in the UK test - waiting 7 days?

I did my life in the UK test today and ped. At the end the woman said that if I am posting my application I need to wait 7 days. My visa runs on Thursday so I can't wait 7 days otherwise it will be submitted too late. Does anyone know why this is and what are the implications of not having waited 7 days? (I have the certificate to send off with my application to say I've ped). Is there a chance they might reject it on this basis and I'd have lost 750 quid straight up? Thanks