As a rule of thumb, try to book a flight that has at least a 90-minute to two-hour connection time, if not more, and don't rely on your airline's reservations system to ensure you have enough time. When booking, consider whether you're connecting at a large or especially busy airport, and if you are, plan a longer connection. If you're traveling on several different airlines, leave yourself even more time. Personally, I'd rather grab a snack or read a book while I wait for my next flight instead of worrying that I'll miss my connection.
For Changi, I will use 2 hours, in case you get flight delays.
The airlines will not be responsible if you miss a flight.