Marked time is a phrase that is commonly used to describe repetitive and unproductive actions. However, there are several alternatives that convey the same sentiment, but with different nuances. For example, treading water or standing still implies a lack of progress or growth. Similarly, spinning one's wheels or going through the motions suggests a sense of stagnation or pointlessness. Other synonyms include biding time, passing the time, killing time, and twiddling one's thumbs. Ultimately, the choice of synonym depends on the context and tone, but all convey a sense of unproductivity and wasted potential.