The phrase "late on" is commonly used to refer to a time that is towards the end of an evening or day. However, there are several other synonyms that can be used to convey the same meaning. For instance, "past bedtime", "after hours", "into the night", and "late into the evening" are all phrases that can be used interchangeably with "late on". Additionally, "toward the end of the day", "late in the night", and "close to midnight" can also be used as synonyms for "late on". Using these synonyms can help add variety to your writing and make it more engaging for the reader.