an hour and a half或者 one and a half hours
two hours and a half/two and a half hours
用is,因为时间不可数,虽然小时可数：
离天亮还有两个半小时.
It was two and one-half hours to dawn.
你的展示预定在一个半小时之后开始.
Your demo is scheduled to start in an hour and a half.
世海明天要/会学中文学一个半小时.
Tomorrow Shihai will study Chinese for one and a half hours.