Actually, that is the average time it takes to just start REM sleep:
https://www.webmd.com/sleep-disorders/sleep-101
“the average time”
Did you perhaps forget that “average” doesn’t mean “minimum”?
Actually, it varies by individual and circumstances such as perceived stress prior to nap. When I was a PhD candidate in neuropsychology, 90 minutes was stated as baseline for REM cycle based on EEG.