Seller allows 30 day returns, e-bay wants me to ship now, why?

[nsykyto]

Seller offers 30-day returns.

I requested a return as soon as I got the item because it didn't fit my car.

I received an automatic email from e-bay saying I have to return the item in the next few days, way before the 30 day window, otherwise I'll lose my refund.

Why is that? When I start a return on Amazon, I can ship the item anytime within the 30 day window.

Do e-bay sellers offer 30-day returns or not? Next time I'll only request a return on the 25th day, what difference does it make for the seller?

Thanks.