i think 4 days in Singapore is too long, but if ur coming during festivities like the F1 season, Chinese new year or christmas, be sure to stay a few more days to experience the local culture.
Also try visiting places like toa payoh and jurong. These are places where u can immerse yourself in the local singaporean culture. Being a Singaporean myself, these are places where i grew up and provide me with the inspiration to do what i do.