Build-To-Order was introduced in April 2001, currently BTO sale launches are in February, May, August, November. Future BTO locations are announced 6 months in advance. This table shows BTO names, town, launch date, estimated completion date, number of units breakdown by flat type, selling price ranges, etc.
HDB InfoWeb Appliation Status page does provide the application rate for last BTO project and SBF, breakdown by flat type. I compiled an Excel table with a summary of application rate for every BTO and SBF launch from 2010 to present and offer it for free download together with HTML pages.