I've learned about separable verbs, 离合词. I learned that separable verbs such as 游泳 must be divided into the verb (游) and the object (泳) when particles like 了, 过, 着, etc. are attached to the verb or the sentence has time-measuring complements like 三个小时. Now I'm wondering if I can combine it with some time-related elements.
For "He swam for three hours", are those two sentences fine?
Apart from the above question, one more question came across my mind. My teacher explained to me that 的 can mean "even" that emphasizes the long duration of an activity by giving a pair of two sentences 我坐了一个小时火车 and 我坐了一个小时的火车. The structure of the former (我坐了一个小时火车) looks very similar to 他游了三个小时泳. So if I put a 的 between 三个小时 and 泳, thus 他游了三个小时的泳, would the 的 make a difference to the meaning of the sentence likewise?