+   uint32 MIN_EXECUTION_DELAY = uint32(1 hours); // whatever

    function setExecutionDelay(uint32 _executionDelay) external onlyOwner {
+       require(_executionDelay >= MIN_EXECUTION_DELAY, "Don't do that");
        executionDelay = _executionDelay;
        emit NewExecutionDelay(_executionDelay);
    }
