There is a setting called "Arm Stay - No Delay" which is on by default. The setting is designed for convenience while the user is at home, and all doors are already secured and just wants to arm the system. When pressing Arm Stay, the system will immediately arm the alarm for your exterior doors and windows. You can disable the setting "Arm Stay - No Delay" in the installer settings --> Installation --> Security and Arming menu. Once disabled, selecting Arm Stay will give you the normal exit delay timer.
Also make sure any opened sensors are automatically or manually bypassed in order to avoid an Exit Fault, which results in a pending alarm.