I tried to fly by VietJet to Bangkok a couple of months ago. Always used AirAsia, Thai Airways and BKK Airways before. So I arrived to check-in counter 52 min before flight (because I spent 20 minutes a night before flight trying to checkin online and I didn't find a way how to do it).
So guy on a counter just said that check-in time is finished and he can do nothing with it. I tried to ask him where I can see airlines rules and he answered of course - go to our website. The problem for me was I had important meeting in BKK that morning. But VietJet staff refused me to pass check-in 50 min before flight. So I came back home. And my plane still was at the boarding gate for 40 minutes more)
At the same time I always arrive at the airport 45-50 min before my flights to BKK by another airlines and I never had any problems with that for 8 years (my house just in 5 minutes from airport). So guys, just be careful with their check-in policy) and good luck.