As long as you are giving around six hours between doses then you should be fine. As mentioned, the reason for taking with meals is to assist with some of the unpleasant side effects like nausea. In simple terms, all drugs have a "life" within the body after which the liver has usually eliminated them (which is why you may need to take pain meds every five or six hours).
Metformin was originally researched as a weight loss drug, but while it proved commercially unsuccessful in that respect, they found that it did assist most Diabetic II sufferers in controlling glucose. The original weight research was as the result of finding that some obese individuals are missing a particular hormone receptor which passes the message that one is "full" and therefore do not need to eat. It would appear that less than 5% of the obese population are actually missing the receptor. This is why a few people on Metformin experience a drastic lack of appetite and so are able to very successfully lose weight on the drug - over 95% will not.
Personally, I was diagnosed DII over sixteen years ago but diet controlled well until four years ago. Being my elderly mother's carer, I didn't have time to deal with it. Not a good move. I subsequently started with Metformin four months ago. I take slow release 2x500mg twice at day.