A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
My interpretation of the info in the link you provided is that m can be used when preceded with h so when used in combination with hours it is valid. It all works for me that way.
Your interpretation is correct and yes, it works on most systems.
I've stumbled upon this problem myself in the past, so I can say that "m" doesn't always work on all systems, but "n" always works.
I should have said "you should" than "you must", sorry, my bad.
Andreas.