As long as one does actually understand the limits of what one is issued feel free to call 90 days three months
On two occasions different American persons I was to at least hang out with in CM for dinners, set themselves up for overstay because they convinced themselves who knows how, that were to be issued a free "one month visa on arrival" at the airport.
Of course they didn't know the day of arrival is day 1, over in a few hours, 31 day months, leap year...