A Singapore visa is not an immigration pass. It is a pre-entry permission for the holder of a valid Singapore visa to travel to, and seek entry, into Singapore. The grant of an immigration pass will be determined by the ICA officers at the point of entry. Possession of a valid visa alone does not guarantee entry into Singapore.
The period of stay granted is shown on the visit pass endorsement given on your passport and it is not tied to the validity of your visa.