Contagem de tempo does not have any end date. It states the current situation for the date of issue. The text differs from AIMA to AIMA, but in general it says the following:
“For the purpose of citizenship, XXXXX is the resident of Portugal since XXXX (date), he/she also is a holder of residence card number XXXXX with the expiry date XXXXXX”.
Apparently, if the card mentioned in the Contagem de tempo expires, the document does not have any value anymore, because both IRN and AIMA treat the law in a way that the applicant should continue be resident/have residence card until receive citizenship. Card expiration does not affect the application after you passed the check point, but before all requirements were checked it is advisable to maintain yr residence permit.