Would appreicate recommendations on where to drink beer and/or eat at some atmospheric old taverns. hoping to avoid tourist traps with high prices and poor service. Thought that would be a good first night activity. However, given that we would be jet lagged, was hoping to do it early, say around around 1800. Thoughts?

You probably want some place near your hotel because if you are jet lagged, you won't want to have a complicated journey back to where you are staying.

That said, a stroll around this street might work for you if it is close to your hotel.

http://www.spottedbylocals.com/madrid/cava-baja/

Restaurant Botin?

I like Casa Alberto from 1827. Genuine Madrid restaurant, still very popular with locals. Try de Rabo de toro or the Carilleras. http://www.casaalberto.es/en/
http://11870.com/pro/casa-alberto
http://www.lonelyplanet.com/spain/ma...h/casa-alberto

18:00 is tough, not too many places will be serving too much food at that hour. I don't think too many places on Cava Baja, in the link above, will be open. Better to go around 20:00 (and you will still be early.)

You can always get a beer in Plaza Santa Ana, almost anytime of the day or night.

Didn't see that 18:00 part. As all normal restaurants Casa Alberto wold not open until 8pm, and most people don't go to eat before 9-10pm. But Cerveceria Alemana - Hemingway's old favourite - close by will be open, and I think they also serve food as early as 6pm. Popular with tourists, but not touristy: http://www.cerveceriaalemana.com/main/

Hemingway? Did he not die a few years ago? has nothing changed over the years ;-)
I do hate it when someone promotes his wife's website.

Bodega de La Ardosa (est. 1892) on Calle Colón 13, closest Metro: Tribunal. Recommendations: Pilsen beer, tortilla, salmorejo.
http://laardosa.es/

Thank you all for the feedback

I think we will do a late lunch and turn in early the first night in Madrid