... where he could have a good time just sitting and watching. (Para. 8)
Meaning: ... where he could enjoy himself by just sitting and watching.
Notice that "have a good time" is followed immediately by -ing verb phrases without any preposition in between. In English "have a good (hard, difficult, etc.) time" is usually followed directly by -ing verb phrases without using any preposition. Look at the following examples:
I had a hard time finding you. 我費好大勁才找到你。
She had a difficult time persuading him to accept the job. 她好不容易勸說他接受了那份工作。
In Spain she had a good time swimming and sun-bathing on the beach. 在西班牙, 她又游泳又在海灘上曬太陽, 過得很愉快。