Hi mojo, thanks for writing to us on AskGuru.
You will need to use cash to pay the stamp duty within 2 weeks of exercising the sale and purchase agreement or the Option to Purchase (OTP). Subsequently, you can apply for a one-time reimbursement from your CPF account together with your application to use your CPF savings to buy a property. Depending on the response time from your lawyer and the CPF board, drawing funds from your CPF account can be a lengthy process. More details here: https://www.cpf.gov.sg/members/FAQ/schemes/housing/housing-scheme/FAQDetails?category=housing&group=Housing+Scheme&ajfaqid=2185416&folderid=11314
Hope this answers your question.