A day trip by train is possible but it would be very rushed as the first train only gets in about 09:45 and the last departure southwards is at 18h51.
The other problem is that Albufeira station is at Figueiras about 8 kms from Albufeira itself. This means having your own hire car, using a local bus or a taxi.
Your better bet would be to take an EVA Transportes bus from Albufeira Bus Station (Rodoviario) which is much closer to the centre.
On weekdays there is a departure from Albufeira at 06:55 arriving Lisbon Sete Rios Bus Station at 09:45.
There is a return trip leaving Lisboa Sete Rios Bus Station at 20:30 arriving Albufeira at 23:10.
These buses are fairly new and the drivers usually v. good. The trip is by motorway most of the way.
Additionally, the metro line from Sete Rios in direction of Stª Apolonia will take you straight to Rossio which is the centre of Lisbon.
Return Ticket would be about 34,20 €
There is another Bus company operating the route RENEX but their terminal is further out of Lisbon at Gare Oriente.
