I am not sure on time limit - perhaps 15 days? I only say that as this is the time allowed to return any items that are faulty etc...
They usually give a refund (or at the very least a credit note for the store) immeidatley.
The main time I have used the hoja, was after being sold a printer for my computer and it turned out not to be compatible, even though I had asked the advice of the shop assistant. I kind of remember (it was some years ago now), that for some reason I did not take the printer out of the box for at least a month (over the 30 days). When I found out it was not compatible, I took it back to the store (Boulanger - now Worten), and they refused to refund my money (or even give me a credit note.) I demanded the hoja, filled it out - and they still refused. A stiff letter to them and the threat of taking the matter up via the OMIC (consumer office - who arbirtate in some matters)... they finally agreed to a full refund.
But it was touch and go!
The other times I have filled out reclamaciones (same as hoja) was by recorded burofax (only way to do an official complaint against some bigger co's).... against Telefonica for refusing to install us a landline - after the engineers site visit had said it was OK.
They never responded (surprize surpirze), and we never follwed it through - too much wasted energy. + we found another supplier.
The OMIC are great for general advice on consumer matters and yes, it is taken seriously (in general) by companies if you get them involved and it is usually resolved before it reaches that stage.
(Eg - some friends who came on holiday to visit me rented a car - they were told to return the car with an empty petrol tank - but were over charge - as we all know! Eu60 instead of the Eu30 it actually is. They did the hoja before leaving the country, and their credit card was refunded the difference. Result!) But if they had not known about it via me - they would have been stung.