There is no single perfect time—your goal and stomach tolerance guide timing. If you have a sensitive stomach, taking magnesium with food can reduce the risk of cramps or diarrhea. For sleep support, many people prefer evening use because it fits a relaxation routine. If muscle cramps after exercise are the issue, splitting the dose (morning/evening) may improve tolerance. A key rule is to separate magnesium from certain medications that have absorption issues (for example, some antibiotics or thyroid medicines) by a few hours. Also, dividing the dose can be gentler than taking a large amount at once. Beyond timing, dose matters: overly high doses can cause diarrhea regardless of the hour.