Sack time, also known as nap time or downtime, refers to a period of rest or relaxation. Antonyms for sack time might include activities that are active, engaging, or stimulating. These could include exercise, work, or socializing. Rather than taking a nap or lounging, activities like hiking, cleaning, or going out with friends would be considered the opposite of sack time. While rest and relaxation are important for recharging and reducing stress, it's also important to balance them with more active pursuits to keep our minds and bodies healthy and engaged.