I never heard of any waiting period before but do take note that you must be a Singaporean and at least 35 years old to apply under Single Singaporean Citizen Scheme.
If you are not eligible under this scheme, then you must be above 21 years old in order to be eligible to purchase a private property. I can introduce bankers to advise you on your in principle approval (bank loan)
Feel free to contact me if you need assistance.
Looking forward to hear from you soon!
M: (+65) 9111 5171