The railway line in question is the Linha da Douro which runs from Porto São Bento to Pocinho. The timetable is available in pdf format from Portuguese Railways at www.cp.pt.
Select from the left hand menu ->viajar em portugal->regional->horarios e preços
then select from the centre panel:
Regionais and InterRegionais
You will then be presented with a list of services
select:
Porto/ Régua / Pocinho
You will then be offered the option to download the timetable for the service which is easily readable.
If you are unable to download send me you email address and I will email it to you. Transit of the whole line from Porto to Pocinho takes 3,5 hours.
Also see this site:
http://www.douronet.pt/default.asp?id=63&mnu=63
There is a lot of info here but the english translation is done automatically by google and is a hoot! But worth pursuing.
Also see this site:
http://www.portotours.com
and specifically this link which i think may be what you are looking for:
http://www.portotours.com/indexen.php?op=catalog&method=detail&idCategory=2&idProduct=9
