The cut-off for check-in relates to the revised departure time. This is standard with every carrier I have ever flown with.

Travelling with kids (done that, and throughout Asia), you really need to ‘roll with the punches, especially if you choose to save money and fly on a LCC and the attendant greater chance of delays and long lines.

I’d prefer to have flown PG or TG/WE where there is a lounge and (generally) good on-time performance - all aimed at reducing stress for my wife and kids. We have also found Nok Air to have been a kind of LCC+. Maybe that is because we fly to visit family so going to non-tourist locations UBP, UTH, SNO.