Not sure where you're getting the 40, anywhere I can find says 39. Why round up when it's so much closer to down though? Maybe the package/Gskill site rounded down?
Also, it's a little off for more than just that timing. Here's a lower one.
My RAM has 16-16-16-39 timings, but hardwareinfo says it's 16-16-16-40.
INFO:
RAM: 1x 8gb Gskill F4-2400C16S-8GRS DDR4-2400 SODIMM
HWiNFO version: 7.06-4500 64-bit (portable)
Debug file and report here https://www.mediafire.com/file/nyiqj8yli6z5kql/files.zip/file
(It wouldn't let me upload...