If flight is from domestic airport I.e. terminal 1D then you need 10min less time to reach comparison to international terminal 3. If train arrives on time then you should book a OLA cab and from Delhi cantt rly stn you will reach Domestic airport by minimum 20min and 30min fr international airport maximum. You should reach check in counter by 1hour before prior to dep and I think you should get your flight depending on your train ontime arrival easily.
All the best.