Hi, adreno and hixxy.
The concept of mean elimination half-life is more appropriate to a xenobiotic drug than to an orthomolecular nutritional substance that is normally used by the body.
Drugs are viewed as toxins by the body, and it works to eliminate them. Nutritional substances are used in the body's metabolism, and the cells import them from the blood, store them to some degree, and use them.
The mean elimination half-life of a drug is usually evaluated by taking sequential blood samples to determine the time required for its concentration to drop to half its maximum value. In the case of methylfolate, if a large dosage is given, the excess will be excreted in the urine with a relatively short half-life. Maybe that helps to produce the three-hour number they cite. But meanwhile, the cells have taken in what they need, so it isn't as though it has all been lost after a few half-lives. More frequent dosing may help a little, but not as it does with a drug.
With drugs, the dosing schedule is set up to counter the body's detox system, so that a therapeutic concentration will always be present in the blood. This works out nicely for the producers of the drug, because the person has to keep taking it, and thus has to keep renewing their prescription. When this is combined with the patent system, and the treatment only of symptoms in the case of chronic diseases, it has the makings of a very profitable setup.
Best regards,
Rich