The goal with immersion is really for your brain to get used to this new world of making characters and to constantly try to improve on your work. You might not have ZBrush around all the time, but luckily, you’ll be surrounded by people (characters) and often animals (creatures), so you’ll have plenty of opportunities to observe and improve even when you aren’t sculpting.
A fair bit of the hard work is actually done while you aren’t technically creating characters. If you see an old man in the street with a giant backpack and a tiny dog, you should observe him. Do you have a pet? Observe! The more you can observe, the better it is, as you’ll increase your visual library significantly this way.
One of the key issues people are making when creating art is to not observe, and it cannot be stressed how important this is. By really immersing yourself in characters and creatures, you’ll gradually get an intuitive understanding of how they work – both from a mechanical point of view in regards to anatomy, but also in terms of how people behave, fashion and general designs.