I saw this on reddit! Happy to be able to congratulate you on the clever idea and nice execution on a less crowded forum.
For those who haven't tried it, this isn't as simply as figuring out X seconds/number, CCCA's calculator is actually looking at the number of syllables in each number as the numbers get larger, because it takes a lot longer to say, for example, seven-hundred-fourty-two-thousands,eight-hundred-and-twenty-nine than to say one-million.