I recently had a connection from T3 (EVA Air) to T4(the new LCC terminal) and had allocated 3 hours. It took less than 1 hour. Every step was fast and efficient, particularly at T4 where they have installed automatic check in terminals and automatic immigration terminals. It literally only took a minute to go through immigration. They are encouraging folks to go the automatic route so there were lots of folks there to assist. Common sense still says to allow plenty of time for that one instance when there are delays, but if your only choice is a short transfer, changi is the one place where you can probably make it work.