Have a look at this article on my blog.
http://barlaventostravelblog.blogspot.com/2009/06/lisbon-airport-to-albufeira.html
You will not have enough time to catch the 20:30 bus to Albufeira Centro.
However, there is a Rede Expresso bus from Lisbon Sete Rios to Albufeira Bus Station about 1km from the town centre as follows:
Dept: 22:30 Arr:01:30
Only runs between 1st June and 15th Sept.
Be aware that there may be no taxis available at the bus station on arrival owing to the late hour. You should probably arrange to be met.
Renex.pt also have a 01:00 departure from Lisbon Gare Oriente Bus Station arriving Albufeira 04:30. (Not Saturday Nights.)
Timetables: Download timetables via my blog as indicated above. (RENEX Bus Service - Lisbon to Algarve timetable)
