The problem with this challenge is that I don't even know where to find the formal write up of the functions. I found this page https://help.alteryx.com/2018.4/Reference/Functions.htm but this does not list all the arguments that can be passed to u.
The examples show how Months, Hours, Days, so I could figure out Seconds, but what if there are other functions there? How can I learn about them? What about micro seconds? I think all the words that can be passed to u should be listed there. Good tip about int16 or int32 potentially not being able to hold enough seconds though.