have a good time的用法主要有以下几点：
1. 表示玩得开心：have a good time的意思是enjoy oneself greatly，常用来表示玩得开心或者享受一段美好的时光。例如："We just hang out and have a good time."。
2. have a good time (in) doing sth：表示在做某事的时候经历了一段美好时光。例如："I believe I will have a good time working with them."。
3. 同义替换：have a good time可以被替换为enjoy oneself, have a great time, have fun, have a ball等。