SELECT STUFF(STUFF('84936',3,0,'-'),6,0,'-')

SELECT STUFF(STUFF(RIGHT('0' + '84936', 6),3,0,':'),6,0,':');

08:49:36

SELECT CONVERT(DATETIME, STUFF(STUFF(RIGHT('0' + '84936', 6),3,0,':'),6,0,':'));

1900-01-01 08:49:36.000

declare @t varchar(6) = '92845';
declare @fullt char(6) = RIGHT('000000' + @t,6)

select DATEADD(second,
     SUBSTRING(@fullt,1,2) * 3600 +
     SUBSTRING(@fullt,3,2) * 60 +
     SUBSTRING(@fullt,5,2),0)

1900-01-01 09:28:45.000

declare @t varchar(6) = '134524'
select CASE WHEN len(@t)=5 then convert(datetime,convert(varchar(10),CAST(getdate() as date))+' '+'0'+LEFT(@t,1)+':'+SUBSTRING(@t,2,2)+':'+SUBSTRING(@t,4,2))
else convert(datetime,convert(varchar(10),CAST(getdate() as date))+' '+LEFT(@t,2)+':'+SUBSTRING(@t,3,2)+':'+SUBSTRING(@t,5,2)) end