It is possible to travel Santiago to Lisbon by train in 11 hours, although it requires changing trains in Vigo and Porto. Currently there is a train departing Santiago at 06:14 into Vigo at 7:41. This will get you onto the morning train from Vigo at 08:58 that reaches Porto at 10:20. Next a train departs Porto at 10:38 that could get you into Lisbon at 14:00. Renfe sometimes shows the route from Santiago to Porto, and sometimes shows no connection.
We did most of this southbound trip last year: mainly because we weren't allowed to enter Portugal directly by air from Canada, and so we "sneaked" (legally) into the country by flying into Spain, and then travelling by rail into Portugal.
We took the Vigo 08:58 train to Porto to arrive at 10:20. (Remember this will be 11:20 Spanish time). So the trip is not a fast one. And it is a small, oldish train with no café or other facilities.
Thus I recommend, if you do this trip, taking the 11:32 AP train Porto Campagna to Lisboa Oriente (for airport) or Lisboa Santa Apolónia (for downtown) for your next train, rather than the 10:38 IC (earliest connection). AP trains are faster, with less stops, so you arrive in Lisboa only 1/2 hour later than with the IC, and have time for a morning coffee and snack in the very nice café right next to the Porto Campagna railway station before you board the Lisboa train. (Then, if you're flying out sometime soon, de-train at Lisboa Oriente, and you're only 3 easy Metro stops from Lisboa Airport.)
That's what we did (took the 11:32), and it worked out well. We only went as far in Portugal as Entroncamento, since that's the closest main-line station to Barquinha.
