There is actually no station called Armacão da Pera. There is a Station called Alcantarilha/Armação da Pera but it lies inland 7,5 km.
Buses are operated by Eva Transportes (http://www.eva-bus.com) as follows:
Armação de Pêra to Alcantarilha(Est)
06:30 06:55 weekdays only (except public holidays)
12:30 12:55 weekdays only (except public holidays)
16:40 17:05 weekdays only (except public holidays)
16:55 17:00 weekdays only (except public holidays)
18:30 18:55 weekdays only (except public holidays)
I would be careful if planning to use this service as it may be linked to daily school runs and may be subject to alteration.
