Liberia to Malpais

The route you describe is probably going to be faster than the bridge/ferry. We went both ways a few weeks ago and you'd have to hit the ferry perfectly to beat the route down the peninsula.

It took us almost exactly 4 hours from Santa Cruz to Montezuma and you'll have to add half an hour for immigration, customs and car pickup, an hour for the airport to Santa Cruz and another forty minutes from Cobano or Montezuma (depending on the route you choose) across to Mal País.

That's six hours and ten minutes putting you in about 30 minutes after sunset at 5:57. That last section isn't one I'd want to drive after dark if I didn't know it pretty well.

Forgot road conditions.

Down the Peninsula
Reasonably good pavement except for
Construction and some gravel stretches from the Carmona turn off to Lepanto
Rough going but possible in a 2WD from Naranjo to just north of Paquera
Rough gravel road from Cobano to Mal País -or- easy 4WD from Montezuma to Mal País

Via Ferry
Actually if you want to take the ferry the bridge doesn't make any difference cause you'd head northeast to Liberia, catch the Pan American all the way to Puntarenas without ever seeing the bridge. That's all reasonably good pavement except for the last leg into Mal País

Getting to Mal Pais

The road south and east of Nicoya to Tambor can be a really bad stretch...going via the back roads is not easy either, as you have rivers and creeks, and poorly marked roads....the ferry is the most straight forward, but then again, can take longer if you dont hit the ferry within a 1/2 hour of departure...

I prefere the road Santa Cruz - Naranjo - Paquera - Mal Pais. The road may be in some parts in bad condition, but a 4WD will manage it.