It is sufficient if you are at the airports in HKT and CNX 2 hours (minimum 1.5 hours) before international departure and 1.5 hours (minimum 60 min or 45 minutes with OLCI and no luggage) before domestic departure
that's sufficient for check in and security (for internation additional outbound immigration)

the additional hour came from the restart after Covid, when airports and airlines did not have enough ground staff, but that has been overcome by now...

in Chiang Mai it is 15-20 minutes from the old town to the airport and 10 minutes during early or late hours if no traffic; in Phuket 45 minutes from the airport to the town and 60 minutes to the beaches in the south (Patong, Kata, Karon etc.)