When referring to a length of time, instead of using the phrase "long durations," there are many synonyms that can be used to express the same meaning. Some other options include "extended periods," "prolonged stretches," "lengthy spans," "long-term," "sustained periods," "continual durations," and "extended timelines." These phrases all convey the idea of a significant amount of time passing, and can be used interchangeably depending on the context. Choosing the right synonym can add variety to your writing and help to avoid repetitive language, while still conveying a clear and precise message.