When you remove fat, the skin almost alweays becomes more loose, if you are talking about tensile strength and elasticity unless you generate enough subdermal scar tissue. However, most patients are referring to their contour when they are concerned about looseness. Looseness from hanging, excess skin is not the same as looseness from loss of tensile strength and elasticity. You might have a flat abdomen with skin that is loose and pliable, sort of like a form-fitting silk shirt which is different from that same form-fitting shirt made out of rubbery wet suit material. Or, you can have a hanging abdomen from tight skin as many beer-drinkers have, like a heavy, over-stuffed winter coat. When you take the "stuffing" out, what happens to the skin depends on the intrinsic tensile strenth and elasticity. How much you take out will also affect the contour. Each situation is different. If your fat pocket is relatively "juicy" with a sense of firmness, then removing fat will allow the skin to "shrink". If it feels more soft, the skin might not shrink as much.
The other question of your history of the pocket of fat and when to do liposuction is even more important. You should be in a healthy, stable lifestyle as far as exercise, level of activity, habits, and diet is concerned. If you have gained weight which is why the pocket of fat is there, you should ask yourself why you have gained weight and what changes in your lifestyle are healthy and sustainable. You shouldn't lose weight just in order to get liposuction, you should improve your health as much as you can and then reassess your body's contour and then see what additional improvements you desire. that plastic surgery can offer.