Those that take metformin will address your timing question. Here is some information on chromium polynictionate.
This is from www.cellhealthmatters.com
Chromium Polynicotinate versus Picolinate
Chromium Polynicotinate has greater biological activity than other forms of Chromium, including sources from picolinate. CP helps to stabilize blood sugar levels and can be critical to the synthesis of cholesterol, fats and proteins. Chromium polynicotinate consists of pure niacin-bound chromium, identified by United States Government researchers as the active component of true GTF (Glucose Tolerance Factor). GTF is responsible for binding insulin to cell membrane receptor sites. Chromium polynicotinate has been shown to possess greater biological activity than other chromium picolinate weight loss supplements.
Chromium Polynicotinate is a mineral required for regulation of blood sugar. It is involved in the metabolism of glucose and is essential for energy. The ability to maintain stable blood sugar levels is threatened by the lack of chromium in our soil and water and by a diet often high in white flour, refined sugar and junk food. Supplemental chromium has been used successfully to control cholesterol, promote the loss of fat and increase lean muscle tissue. Hoodia Slow carb formula uses a form of chromium that is readily absorbed into the blood. In fact, the niacin bound chromium is a much more effective form of supplemental chromium than the more common and cheaper chromium picolinate.
Chromium polynicotinate facilitates and/or stimulates the metabolism of sugar, fat and cholesterol in the body, as well as the function of insulin. Major hospital and university studies have suggested that supplementation with chromium may reduce body fat, help build lean body muscle, regulate blood sugar and lower elevated cholesterol, particularly in chromium deficient individuals. The polynicotinate and amino acid forms of chromium found in our Hoodia trim fast Slow Carb formulas are the most biologically active, most potent available.
Chromium plays a role in the metabolism of glucose, and is necessary for energy production. Since this mineral assists in the production of insulin, it helps to stabilize blood sugar levels and can be beneficial both for people with hypoglycemia and diabetes. It is also crucial to the synthesis of cholesterol, fats, and proteins. Chromium Polynicotinate is more effective than any other type of chromium, as it binds the elemental chromium to niacin (Vitamin B-3). This provides a biologically active form of chromium, which is more absorbable in the body.
Chromium Polynicotinate has been recommended by the U.S. Government National Research Council as the superior and preferred form of chromium for bioavailability and biological activity, thus the reason we use this form of Chromium supplement (as opposed to picolinate) in our Hoodia Slow Carb special weight loss formula.
Deficiencies in chromium are rare because this mineral is readily available in the foods we eat. However when deficiencies do occur it may be associated with glucose intolerance and/or insulin resistance.
Is Chromium Safe and are there side effects?
The typical safe adult dosage of chromium is 50 to 200mcg daily, taken with food. However, those supplementing with chromium as part of a weight loss program have been known to take up to 400mcg daily.
It's very important not to take too much chromium, individuals who have exceeded 1,000mcg daily for an extended period of time have experienced kidney failure, liver dysfunction, anemia, renal failure, and blood abnormalities. Since chromium is regularly included in many multivitamins it's important to read the labels of all dietary supplements consumed to ensure safe chromium levels are not exceeded.
There are few side effects when supplementing with chromium, however some people may experience mild gastrointestinal upset.
Safety issues concerning the use of the picolinate form of chromium have been in question for the past few years. Aside from genetic damage, picolinate is known to "break off" from its chromium-bond and cause adverse effects. Chromium picolinate is a patented version of the trace mineral chromium. Picolinic acid is produced in the human body, apparently for the purpose of improving the cellular uptake of trace metal ions. Scientists have demonstrated that several minerals in picolinate form are better assimilated than most other forms of the same minerals.
Chromium polynicotinate is a well assimilated form which may have more benefits for certain conditions than does the picolinate form. Chromium polynicotinate seems to have some definite advantages over chromium picolinate, including even better bioavailability. It now appears that niacin-bound chromium is a safer form of chromium for supplementation. Some studies have also shown that niacin is necessary for chromium supplements to be of benefit.