Ah. OK. Metformin doesn't work that way. It works by helping to reduce the amount of natural glucose produced by the liver and sent to the blood stream. It also helps a little bit with insulin resistance. It is mainly an appetite suppressant. so it helps overweight people the most. It doesn't do anything to stabilise blood glucose. It also accumulates in your body and doesn't "run out" every day like some medicines do. As long as you take the Metformin with food, it doesn't matter when you take it or when you eat. Does that help?
Metformin does not work like insulin or other medication that induce insulin production.
It works by reducing glucose production by the liver and reducing insulin resistance allowing the body to make better use of its own insulin.
Consequently you do not take metformin is response or in preparation to a meal. You take it at fixed times as prescribed by your doctor and it then acts throughout the day.
So in answer to your question you do not have to eat within a fixed time of taking metformin.
As metformin can cause upset stomachs as a side effect for some people, it is customary to take metformin with a meal as this has been found to reduce the chances of stomach upsets.
metformin only slows the speed our liver transforms proteins into glucose, and maybe works a little in other areas of the
body..
as an illustration, one could say that metformin only works for around 10% of lowering one's insulin so that all the 90 % is only helped by drastically changing ones diet by avoiding carbs.