Many start a diet with the hopes of looking a certain way but don't realize that weight loss alone just means you will be a smaller version of yourself. If you really want definition, you've got to build the muscle underneath first. So depending on how much lean mass you have, how often you are working out, and the type of training you are doing, how long it will take you to get ab definition will vary. Genetics can also play a role.
For many people, getting shredded requires them to build muscle mass or "bulking" before focusing on fat loss. And that's really it in a nutshell; there are only two requirements for getting a six-pack:
Build abdominal muscles
Lose body fat
And you can't just focus on losing belly fat alone; getting shredded requires losing total body fat - to see more abdominal definition usually requires a lower body fat percentage - around 15% or less for men and 20% or less for women.
This overall process can take many months, if not years. The reality is, many people cannot build a beach body in six weeks, but you can still make drastic improvements in your fitness and health. And with enough dedication and patience, you will eventually get there.
Having this understanding going into it is key. It allows you to be realistic with your expectations and will help ensure you don't get discouraged or give up when results don't come overnight.