This seems to work for all combinations of time values.

Create Table #test (

TestDate varchar(9)

)

Insert into #test

Select '0'

union

select '01:00:22'

union

select '39:00'

union

select '02:19'

union

select '-03:06'

Select TestDate

,case left(TestDate,1)

when '-'

then Convert(decimal(9,8),Convert(datetime,Left('00:00:00', 9-Len(TestDate)) + substring(TestDate,2,8))) * -1

else

Convert(decimal(9,8),convert(datetime,Left('00:00:00', 8-Len(TestDate)) + TestDate))

end as SortDate

from #test

order by SortDate