Technically yes, but it is not recommended as you will spend most of your day in transit rather than enjoying the scenery. Portofino and the Cinque Terre (five villages) are in the same region of Liguria, but they are about 1 to 1.5 hours apart by train. To attempt this, you would need to start at dawn in the Cinque Terre, visit only one or two villages (like Monterosso and Vernazza), then take a train to Santa Margherita Ligure, followed by a ferry or bus to Portofino. You would only have about 2 hours in Portofino before needing to head back. A better one-day itinerary is to pick either the Cinque Terre loop (using the train/ferry to see 3-4 villages) OR a Gulf of Tigullio day (combining Santa Margherita, Portofino, and Camogli). Trying to "see it all" in 10 hours results in a rushed experience that misses the "dolce vita" charm these locations are famous for.