Completing Memory Sequence 4 in under 9 minutes is not too hard. You can complete the sequence in approximately 8 minutes -- so there is some room for error. You should run at all times (do not walk slowly). In the climbing sections, press X to move quicker. The fastest way to kill enemies is to throw a smoke bomb, then perform an assassination while sliding under them. If you took too long during a section, you can restart the checkpoint. Restarting checkpoints does not add to your time.