> Sure, it all seems to work for now... and then a customer signs up from Tuvalu, and performs a billable action at 11:59PM on the last day of the month, and yo

> Sure, it all seems to work for now... and then a customer signs up from Tuvalu, and performs a billable action at 11:59PM on the last day of the month, and your whole billing system falls over because they now have a split invoice generated for next month while it's still this month. You think there's much of an overlap between systems that do time zone arithmetic with naive timestamps and ones that bill in the customer's time zone?