I think shorter than a minute is absolutely legitimate. Punk is one example - Black Flag's "Spray Paint" on Damaged is 33 seconds. Paraphrasing Rollins, it takes the shortest, most direct route to what the song is about and then gets the fuck out. It's perfect.
I also think about Brian Eno, who was tasked with creating the Windows 95 startup sound. He was given this laundry list of emotions that it must convey..."and it must be seven seconds long". This sent him down a whole rabbit hole of micro compositions. If it works for Eno, it works for me.
I think the one minute "rule" is a good guideline....but if the song is purposeful in its short length, go for it!