Do cracks in a new home fall under the developer's defects liability?
Defects appearing within the defects liability period should be reported to the developer in writing. In the standard sale and purchase agreement reproduced in Sandy Island v Thio Keng Thay, the developer must make good defects that appear within 12 months of the purchaser receiving the Notice of Vacant Possession. Some early shrinkage cracking is normal as a building dries out, so photograph and date cracks at handover and during the period.
From the RRD Field Guide, checked against the sources cited in Cracks in Walls, Beams and Ceilings in Singapore: Which Are Structural and When to Worry. General information, not advice for your project.
The fuller picture
Most hairline cracks in plaster, paint and at wall-to-beam joints are non-structural, caused by shrinkage and thermal movement. Worry when cracks are wide or widening, diagonal or stepped, tapered, recurring, accompanied by rust stains, sagging or sticking doors, or appear in beams, columns or slabs. Monitor with dated tell-tales and call a Professional Engineer for those signs.