Hello tji,
Cathay or Eva are both going to tell you 3 hours, but even so I wouldn't risk less than 2 hours for you to get your baggage, move to international, and if you are on a full flight, check in, then immigration CAN take 30 minutes, and you always have to leave 15 minutes in Bkk to find your gate and get through security. If you end up with some time on your hand and don't want to go into town, check what trade fair is on eg homewares, jewellery, food/beverage and if it suits you, cab a cab to the trade fair centre which is close by. Even if you are not in the business, friends I have taken with me have found them very interesting although frustrating as you often can't buy single items. enjoy your travels.