There is a small luggage storage facility at Fátima bus station. I do not know the current opening times.
If you want to be 100% certain of taking the bus you prefer, buy tickets in advance. These are on sale up to 30 days ahead at www.rede-expressos.pt but if you do so you cannot take a different bus without changing your ticket, which may not be possible in certain situations. There are no 'open' tickets.
Thank you! That's very helpful.
You are too early to get tickets for 20 October. They are sold only 30 days in advance. If you go to the Rede Expressos website www.rede-expressos.pt and enter the journey 'origin' and 'destination' without a date you will see the general timetable. When it is time to buy tickets ie not more than 30 days in advance all available times will be listed once the date is entered.
The Porto bus station used by Rede Expressos is at Campo 24 de Agosto next to the metro station of the same name, to the east of the city centre.
I hope this helps.