Ask HN: How quickly do you get paid in your industry or country?

For those who are working for themselves (or handling billing), how quickly do your invoices get paid in your industry or country?

I notice a stark difference in the attitudes to payment terms in different countries that I work in. For example, in certain parts of the EU it seems that if you put "payable within 30 days", you get paid on the 30th, or more likely, on the 30th day you send a reminder and you get paid a week or two later.

When somebody invoices me I interpret "payable within 30 days" as "the work is done, payment is due now, but you have 30 days as a courtesy". I find it incredibly disrespectful when invoices don't get paid on time, or at worst the business doesn't at least explain why payment hasn't been made.

I'm considering to changing all invoices to "payable upon receipt" in the future and would be interested to hear people's experiences with speeding up payments.