@last_run_time is a 9.4. User-Defined Variables and last_run_time datetime one 13.6.4.1. Local Variable DECLARE Syntax, are different variables.
Try: SELECT last_run_time;
UPDATE
Example:
/* CODE FOR DEMONSTRATION PURPOSES */
DELIMITER $$
CREATE PROCEDURE `sp_test`()
BEGIN
DECLARE current_procedure_name CHAR(60) DEFAULT 'accounts_general';
DECLARE last_run_time DATETIME DEFAULT NULL;
DECLARE current_run_time DATETIME DEFAULT NOW();
-- Define the last run time
SET last_run_time := (SELECT MAX(runtime) FROM dynamo.runtimes WHERE procedure_name = current_procedure_name);
-- if there is no last run time found then use yesterday as starting point
IF(last_run_time IS NULL) THEN
SET last_run_time := DATE_SUB(NOW(), INTERVAL 1 DAY);
END IF;
SELECT last_run_time;
-- Insert variables in table2
INSERT INTO table2 (col0, col1, col2) VALUES (current_procedure_name, last_run_time, current_run_time);
END$$
DELIMITER ;