It depends on whether you use the time term as independent qualifier (can't add 在) or as part of a phrase, especially the prepositional phrase (在 usually must be added), and my suggestion is to avoid this type.
我是在1997年喜欢上汉语 vs 我(是)1997年喜欢上汉语(的), 是 and 的 purely for emphasizing;
我在八月到的上海 vs 我八月到(的)上海, again, 的 for emphasizing.
Also, I recommended try to avoid using 在 at the beginning of a sentence whether to introduce time or place, unless you really want to emphasize "among/during":
在北京，八月最热。 在八月，北京最热。 both sound weird, right?