Besides the technological problems that you could have to separate the metabolites from the formulation and the quantitative analysis that will be performed, you have to considerate the following aspects:

If you are using 10 standarized plant extracts it would be convenient to evaluate each referenced metabolite.

if there is a therapeutic indication for your herbal formulation, you could evaluate the stability or concentration of those metabolites with described biological activities.

However it is important to review your country legislation about that specific topic or referred to pharmaceutical products. You can also check: The american herbal pharmacopeia https://herbal-ahp.org/ | the british herbal pharmacopeia https://bhma.info/british-herbal-pharmacopoeia-1996/ | Mexico´s official normativity NOM-073-SSA1-2015 "Stability of drugs, pharmaceutical specialties and herbal medicines" (in spanish).

Greetings

Shelf life can be fixed for 24 months (2 years) for the product, if the herbal formulation is stable when stability tested at 40 deg celsius / 75% RH for 6 month evaluating the drug content and degradation.

Shelf life of the herbal formulation depends on the material nature.

I think the best way to keep your samples in a incubator, maintaining 40 degree C temperature and 75% RH, and analyze your samples every month by HPTLC chemical fingerprinting till the chromatogram similar.

Best wishes

Yes, Dr. Rajesh, you are right. Here, I also want to include that ICH guidelines should follow for the same. Best

follow ICH, WHO and API part 1 vol 9 guidelines for stability study. Physico chemical variation should be more than 25%.

for quantitative: active component may be decided based on its indication, its variation should not be more than 20%