兩種都可以。

一、It"s a waste of time doing sth.

1、It is a waste of time going to the doctor with most mild complaints.

一點小毛病就去看醫生是浪費時間。

2、It is a waste of time warning him — he is determined to go his own way.

警告他等於浪費時間,因為他決心要照自己的意思去做。

二、在非正式的英語中也有It"s a waste of time to do sth.的用法

1、It is a waste of time to read such a magazine.

看這種雜誌真是浪費時間。

2、It is a waste of time to try to rehabilitate some criminals.

改造有些犯罪分子是浪費時間。

相關用法：a total waste of time 完全浪費時間

It is a total waste of time to see soap opera。

看肥皂劇真是完全浪費時間。