You can change the supply period for each product.
reduce it if you want.
but then, a shortage in the country will reduce your supply index and directly with it, the welfare index and production levels in all your corporations.
make sure you have all the products needed for the country in stock.
better not to be dependent on the market. The supplies are essential.
Some materials I buy for 120 months (max).
it does not increase the cost. It changes the cash flow.
profits remain the same and there is no danger of shortages.