You're in for a very long day of traveling AND you have to have everything go pretty much on schedule and without any hangups.
Now, if that happens my friend, (insert laugh track) it's your lucky day.
Some spanish will certainly help too.
IMO, I'd recommend you shoot to get to S.D., spend the day/night get a place to hang your hat and then hit the bricks fresh in the morning.
You could be on a North Coast beach by 10 am. You get to see the capital, and arrive at your destination bright eyed and bushy tailed, instead of later at night, worn out and more than likely a tad frustrated and you just wasted an entire day on a bus.
Save the all day travel for the day you have to leave or if someone's chasing you.