Legal analysis: Brokers' intermediary services cannot be extended indefinitely, so the time limit for brokers to complete intermediary matters should be clearly stipulated in the contract, from a certain day of a certain year to a certain day of a certain year. If the time limit is exceeded, the contract will naturally become invalid.

Legal basis: Article 96 1 of the Civil Code of People's Republic of China (PRC), an intermediary contract is a contract in which the broker reports the opportunity to conclude a contract to the client or provides media services for concluding a contract, and the client pays remuneration.