5 years is very specific.
Its origin is important to know, to interpret that specificity. Did Feynman derive five years for innovations. No? Does the Chinese calendar have five years per “year week”? No.
So where did “5” come from? The Soviet Union.
Now questions about how well 5 years works can focus on historical successes and failures, instead of “where the heck did that number come from?”.
Do you know by any chance if the Chinese have 5 fingers on each hand? Is the number 5 forever tied to the Soviet Union and must never be used in economics again?
Are you proposing that having five fingers completely explains why they chose five years for their plans? Despite five being a number so common, it has innumerable associations beyond our hands?
Ok. Well don't be coy, show your work.