When referring to a specific period of time, the phrase "in interval" can be substituted with a variety of synonyms depending on the context. Words such as "during," "throughout," "within," or "amidst" can all be used interchangeably to convey the meaning of a duration within a larger time frame. Alternatively, "in between," "intermittent," or "sporadic" can be used to describe moments within an interval that are irregular or inconsistent. It's important to choose the appropriate synonym based on the exact meaning you wish to convey, as each has its unique connotations that can impact the overall tone and message of your writing.