In my experience with travel during the 12 days of Christmas, I would recommend you plan on catching the 1505 train ... a few flakes of snow somewhere anywhere always send Christmas period traffic into havoc.
It normally take a half hour from time of deboarding to time of getting your bags. I would allow at least another half hour for passport control, however if all the customs agent do is stamp your passport with a visa then it probably will go faster.
The Metro will take 45 minutes ... too tight.
The bus takes 40 minutes ... depending on traffic ... too tight.
The Cercanias will take 25 minutes and leaves at 0858. The next leaves at 0928 and will arrive too late.
So the time appreciation is:
- 0750 land.
- 0820 collect bags
- 0850 clear customs
- 0858 catch Cercanias
- 0940 catch train
Its tight. You will need to know where to go to catch the Cercanias train. I would suggest that you don't buy a ticket in advance ... any delay will mean you miss the train. Murphy's law applies.
If you try it and get to Atocha Renfe station too late then take the Metro to Avenida de America to catch the ALSA bus to Pamplona.
2006
Madrid Airport to train station Puerto de Atocha
a. Puerto de Atocha is reached by Metro. Take line 8 from airport T1-T2-T3 or T4 to Nuevos Ministerios; line 10 to Tribunal; and, line 1 to Renfe Atocha.
b. Puerto de Atocha is reached by Renfe Cercanias direct from Madrid Airport T4
c. Puerto de Atocha is reached by EMT Madrid Aeropuerto Express direct from Madrid Airport.
2011
Madrid Airport to bus station Avenida de America
Intercambiador de Avenida de America (Madrid) is co-located with the Metro. Take line 8 from Barajas airport T1-T2-T3 or T4 to Colombia; and, line 9 to Avenida de America.
Madrid Metro
http://www.metromadrid.es/en/index.html
Madrid Metro Map
http://www.metromadrid.es/export/sites/metro/comun/documentos/planos/Planomayo2013.pdf
Madrid Cercanias (operated by Renfe)
http://www.renfe.com/viajeros/cercanias/madrid/index.html
EMT Madrid provides Madrid transit bus services
http://www.emtmadrid.es/
EMT Madrid Aeropuerto Express
http://www.emtmadrid.es/lineaAeropuerto/index.html
Intercambiador de Avenida de America
http://es.wikipedia.org/wiki/Intercambiador_de_Avenida_de_América