I think Ebay states somewhere in it's policies that buyers have 10 days to pay.
That's reasonable.
I generally pay within an hour or two of the auction end, but I have had buyers wait 7 or 8 days to pay before too. But that seems to be the exception rather than the rule.
And then you get your people who drink while they are Ebayin' and forgot that they bid on something in the first place. Usually a simple "Perhaps you forgot" note gets them to pay.
But sometime you have to be patient with people. They also may have had unforseen circumstances that delayed their payment.
BTW, once you are finished with a machine and your Ebay auction is finished the machine is just sitting there doing nothing. It's not eating anymore of your time!