The last nap of the day is going to be a catnap (30-45 minutes) until 6-7 months old, is that what you're asking?
As for the other naps, at this age I'm not sure it matters as much as long as you keep last A time the right length. I was thinking more of a toddler who is on 2 naps per day and moving toward 1, adn then you really want that last nap of the day to be longer since they have so few chances to catch up on sleep.