I allow a max time for delivery limit by post of 35 days from OS before telling the seller I want an immediate refund or I open a Paypal claim and leave them a Neg feedback.

I did exactly that with a seller recently, although I didn't threaten them with Neg feedback,  but I did warn him that could we not reach an amicable solution then I would be opening a dispute to get my money back. 

He called me impatient and demanding.... For expecting something to arrive from the US within 30 days..  I informed him that considering he had a fair amount of Negative feedback in relation to slow post, that he should probably look for a more reliable postal service.