Losing weight fitness DVD and cutting out snacks HELP!?

ive done it before by cutting out snacks completely but no exercise.... but now i have fallen into the trap of snacks again! im 100% ready to cut out snacks again BUT have one on a saturday so im not depriving myself this time.... if i do that and do the ministry of sound workout dvd (pump it up 2010 ultimate dance workout) how long do you think it will take for me to tone up! HELP please ive really let myself down.