The best time to try for the slot booking is 8pm IST for the one's who is doing from India. But we need to check on a regular basis, coz I paid the Visa fees and in 3 days I was able to get the slots for the Biometrics and the Visa Interview slots. Please do try to set and alarm for 7:55pm or 8pm and try for it continuously refreshing the page. I opted for a Mumbai VAC because i got the documentation from there itself.