physical presence during last 3 years ( not last 5) ?

[darcy2000]

A friend of mine did his citizenship interview recently, and the officer was counting the days my friend has been out of the country during the last 3 years.
Is there any requirement for the last 3 years ?
I only read that during the last 5 years, you have to be in US for at least 2.5 years, but I am unaware of a requirement for the last 3 years.
Is there one ?

Thanks,

darcy