The holding time depends on the contract of stock index futures. For example, if you buy an IF 140 1 contract, it will be delivered on the 8th today, and 15 can only be held for 7 or 8 days. If you buy an IF 14 12, that is, a stock index futures contract that expires in February, you can hold it for more than 1 1 month.

As for the problem that the delivery time is too short, because the delivery of stock index futures is cash delivery, that is, when the contract expires, you won't really pay for a basket of stocks with one hand, but convert a basket of stocks in your hand into cash, that is, RMB, and then transfer how much you earned or lost, so the delivery time is very short.

The essence of futures is to sign long-term contracts with others to buy and sell goods (or stock indexes, foreign exchange, interest rates) in order to achieve the purpose of maintaining value or making money.

If you think the futures price will go up, go long (buy and open positions), go up (sell) and close positions, and earn: price difference = close positions-open positions.

If you think the futures price will fall, short (sell the position), fall (buy) and close the position, and earn: price difference = opening price-closing price.