Timing your purchase around infra projects: What I wish I knew

My lease ends in 4 months and I still haven't figured this out. I'm eyeing a 3BHK, maybe in Noida Extension or near Yamuna Expressway, budget around ₹1.2Cr. Everyone says Jewar Airport and FNG Expressway will push prices up. But kitna upar jayega, and kab? Should I buy now before completion, or wait for actual impact? Builders like Godrej Properties and ATS already seem to have priced in. What's the real ground reality about timing? Any past experiences with big infra projects impacting property value in Greater Noida?