3 1 day. According to the inquiry of the wealth management house, it is very easy to change contracts for futures about one month after the delivery date. In terms of activity and liquidity, it must be the main contract. First, there are many participants in the main contract, which involves a lot of funds. It is unlikely that a single account will affect the price. It is very easy to open and flat positions. In addition, the chart of the main contract will be more standard.