;with cte as(
select *,row_number() over (partition by userid order by operate_time) rid from tb
)
select * from cte a left join cte b 
on (a.rid=b.rid-1 and datediff(seconde,a.operate_time,b.operate_time)>30)
--没环境，LZ试下，思路差不多，细节自己可以改下

------解决方案--------------------

SQL code
use Tempdb
go
--> --> 
 
if not object_id(N'user_log') is null
    drop table user_log
Go
Create table user_log([userid] nvarchar(2),[operate_time] Datetime)
Insert user_log
select N'a','2011-1-4 10:00:00' union all
select N'b','2011-1-4 10:00:00' union all
select N'b','2011-1-4 10:00:05' union all
select N'a','2011-1-4 10:00:31'
Go
Select 
* 
from user_log AS a
WHERE DATEADD(s,5,[operate_time])<(SELECT MIN([operate_time]) FROM user_log WHERE [userid]=a.[userid] AND [operate_time]>a.[operate_time])
/*
userid    operate_time
a    2011-01-04 10:00:00.000*/