There's a couple of ways that you can do this sea-to-summit. A fit person can reach the summit in 10/12hrs and take the cable car down. Some choose to walk as far as the Altavista Refuge, stay the night, and be on the summit for sunrise. Or, you can walk back down to the Montana Blanca Car Park or the Parador Hotel.
From the beach, there's no real let up on the ascent until you reach about 2,200m. It levels out a bit then, drops about 200m and then it's climbing again until you reach the summit. The route isn't marked but there are tracks all the way.
Left a car at Montana Blanca Car Park on Wednesday, did a water drop near la Fortaleza and walked out to El Portillo to get the bus back down to the South of the island. Took the bus to our accommodation in Los Relaejos on Thursday and got a taxi to Playa Del Socorro on Friday morning.
Stats above are a bit off. There's about 4,200m of Asc. and 1,800m Desc. Didn't really need the water at the drop as carried 2.5l from start but there was comfort in knowing it was there.