Please tell me how long it takes for magnesium citrate to work?

Work for what: Magnesium citrate for constipation typically works within 4-6 hours of drinking 8 ounces. If it does not work there be be a bowel obstruction or exceedingly hard stool in the colon that cannot be bypassed easily, for low magnesium levels in the blood stream it may never work because the absorption may be inadequate due to rapid transit through the GI tract.