When it is time for you to depart Suvarnabhumi International Airport back to your home country, you will need to be aware of a few things.
First, the airport has a weird habit of not opening ticket counters until 3 hours before the flight. This can create a massive jam at the ticket counters.
Once you exit the ticket counters, you will need to proceed upstairs to the immigration checkpoint.
One again, there can be a massive line here as well.
It seems, depending on where you are in the ticket counter line, 3 hours can be rushing it to get through ticketing and immigration.
It can be quite stressful so be prepared for the wait!
Do not worry about TOO much time in the terminal as there is Thai massage, restaurants and shopping to pass the time.
The big issue is getting through ticking and immigration with enough to time to get to your departure gate on time.
Airports of Thailand (AOT) has this page to give you the Flight Status on every flight.