Matt and I did do 2 borders in one day, El Salvadore-Honduras-Nicaragua, and it did turn out ok, barely. The El Salvadore-Honduran border was just a mess and very confusing. Of course we hit it at lunch which doesn't help. We were going to stop short of the Nicaraguan border but didn't find a place to stay so went through. It was pretty easy except they made a mistake in the paperwork so we had to go back to get it straightened out. Unfortunately it was second shift lunch so we got to wait. So two borders one day, both at lunch. El Salvadore-Honduras 3 hours with a helper, best $5 spend. Honduras-Nicaragua 2 hours but without the paperwork mistake it would have been only one hour. We got out of the last border after dark and had a 20 km ride to a hotel. Kind of pretty except for the rain and not being able to see the walkers and bikers. Not really recommended but you do what you have to do.
On the trailing edge of technology - chris