Magnesium citrate typically takes between 30 minutes to 6 hours to work, causing a bowel movement by pulling water into the intestines to soften the stool and stimulate bowel activity. The exact timing varies depending on factors like the individual's digestive system, dosage, hydration level, and whether it is taken on an empty stomach. The effects usually last up to about 24 hours, with complete elimination from the body occurring within one to two days.