By extending their right to reject you may be actually denying them their Statutory Rights.
The Right to Reject means the customer has to prove the fault was present at the time of sale. Whereas after 30 days it is presumed to be present unless the seller can prove otherwise.
So by extending it, to say 60 days, the customer will therefore have to prove it was there for the extra 30 days instead of making the supplier prove it wasn’t.
Whether a fault develops after a week or 7 if it wasn’t there at point of sale then it makes no difference.
The only other real difference after the 30 days is the right to repair.