On-time possession is a myth in Noida real estate?

3 BHK hunt continues. My wife's priority is a safe gated community near a good school. Has anyone had positive experiences with on-time delivery from Ajnara or ATS in Noida? Heard mixed reviews, especially about hidden charges at possession. Should I even consider under-construction with these builders, or stick to ready-to-move? Need some real experiences, not just marketing promises. Kya kisi ko pata hai about post-possession maintenance costs with them?