This is a common question among many triathletes, not just those who are new to the sport. It’s made more difficult by the ‘noise’ from social media and input from tri books, magazines and fellow training partners.
The answer to this will depend upon the length of event you have entered. An Ironman event will require far more training time than a sprint distance triathlon. A principle that I use is to do the minimum amount of training that will allow you to make progress with your fitness.
Depending upon your workout history prior to taking up triathlon, you are likely to benefit from any training that you do. Even 1 swim, bike, and run session per week will provide an overload for a complete beginner. With regards to adequate volume, a good start point is to work out how much training you can actually complete each week.
For example you might have 45-60 minutes each day and 2 hours on a Saturday and Sunday. That would provide a total of 9 hours. However, it would be prudent to have a full day of rest. If you use one of your weekdays for rest, that takes you back down to 8 hours.