I got the solution:
convert(datetime,(
Cast((Left(fwo.Date_Id,4) + '-' + SUBSTRING(cast(fwo.Date_Id as varchar(20)),5,2) + '-' + right(fwo.Date_Id,2)) + ' '
+ (case when len(fwo.Time_Id) < 4 then LEFT(fwo.Time_Id,1) else LEFT(fwo.Time_Id,2) END + ':' + RIGHT(fwo.Time_Id,2)) as datetime)),120) as[Estimated Date Time]