Memory system and operating method thereof

A method for operating a memory system, comprising:

• storing start time stamps of a plurality of tasks;
• determining a delayed task among the tasks by performing a delay check operation based on an end time stamp of a current task and the start time stamps;
• and
• assigning a priority to the delayed task.

A memory device comprising:

• a memory device;
• and
• a controller suitable for queueing tasks in priority and normal queues according to priorities of the tasks, and controlling the memory device to perform operations primarily according to queued order of the tasks in the priority queue and secondarily according to queued order of the tasks in the normal queue,
• wherein the controller moves and queues into the priority queue a task queued in the normal queue when a difference between an end time of a currently completed task and a start time of the task queued in the normal queue is longer than a predetermined time.