HLE must be obtained before OTP...
Buyers need to obtain an HDB Loan Eligibility Letter
With effect from 1 Jan 2007, flat buyers who intend to obtain an HDB loan will need to apply for an HDB Loan Eligibility (HLE) Letter before they can commit to a flat purchase. The HLE letter (which is valid for 3 months from date of issue) must be obtained before buyers exercise the OTP for the flat. Buyers are advised to have the HLE letter even before they look for a flat.
source:
http://www.hdb.gov.sg/fi10/fi10201p.nsf/WPDis/Buying%20A%20Resale%20FlatOption%20to%20Purchase%20for%20Resale%20Transactions?OpenDocument