The Shrine's travel pages say the A1 is the main road and that buses between the main Portuguese cities and Fátima are frequent, with Lisbon services almost hourly; it points readers to the Rede Expressos timetables for current times rather than publishing them. Journey time from Porto by road is not published on the official site; confirm it on the operator's timetable for your date. The bus station's position a few minutes' walk from the Sanctuary is the key advantage over the train.
If you prefer rail, the Shrine lists three stations: Chão de Maçãs (the Fátima station, about 25 km away, taxi or bus onward), Caxarias (taxi and regular buses, recommended for late arrivals), and Leiria, which has a taxi rank and near-hourly buses to Fátima. The Shrine itself notes that the train route ends up longer and more expensive than the bus because the last leg must be covered separately.
A common itinerary is Lisbon for two or three nights, bus north to Fátima for one night so the 9:30 p.m. candlelight procession is not missed, then bus on to Porto; the reverse order works just as well. Drivers should note the Shrine's warning that the parking lots nearest the Sanctuary fill first on the 12th and 13th of May and October, and that it suggests leaving the A1 at Leiria and using the N113 when the Fátima exit backs up. The existing page on Lisbon to Fátima by bus or train covers the southern leg.