The terms of the contract determine when the earnest money must be deposited. For example, under the One to Four Family Residential Contract (Resale) (TREC 20-16, TXR 1601), Paragraph 5 states that the earnest money must be delivered to the escrow agent “within 3 days after the Effective Date.”
If the contract does not state a time period, TREC Rule 535.146 would apply. Rule 535.146 requires that unless a different time period is agreed upon in writing, any trust money, including earnest money received by the broker, must be delivered to an authorized escrow agent (or deposited in a trust account) within a “reasonable time.” The commission has determined a “reasonable time” to be not later than the close of business of the second working day after the date the broker receives the trust money.
Therefore, you should deposit your buyer’s earnest money check in accordance with the terms of the contract or, if the contract doesn’t state a deadline, by the close of business of the second working day after you received the earnest money.