This query does as you as. Difference between two most recent. Dont you want the difference between the start and end of each query though? I inserted you data into a table called test.

Create Table Test([field] varchar(45))

Insert Into Test(field)

values('13 2004-07-13 13:15:26.140 end query 10 0')

go

Insert Into Test(field)

values('12 2004-07-13 13:15:01.263 Start query 0 0')

go

Insert Into Test(field)

values('11 2004-07-13 13:13:31.140 end query 10 0')

go

Insert Into Test(field)

values('10 2004-07-13 13:13:06.997 Start query 0 0')

go

Insert Into Test(field)

values('9 2004-07-13 13:12:19.043 Start query 0 0')

go

Insert Into Test(field)

values('8 2004-07-13 13:11:06.140 Start query 0 0')

go

Insert Into Test(field)

values('7 2004-07-13 12:54:49.607 Start query 0 0')

go

Insert Into Test(field)

values('6 2004-07-13 12:54:34.373 end query 10 0')

go

Insert Into Test(field)

values('5 2004-07-13 12:54:06.500 Start query 0 2729')

go

Insert Into Test(field)

values('4 2004-07-13 12:41:48.157 end query 10 0')

go

Insert Into Test(field)

values('3 2004-07-13 12:41:19.747 Start query 2 0')

go

Insert Into Test(field)

values('2 2004-07-13 12:11:23.793 end query 10 0')

go

Insert Into Test(field)

values('1 2004-07-13 12:10:59.263 Start query 0 0')

go

select (select Max(Substring(field, CHARINDEX(' ', field) + 1, CHARINDEX('.', field) - 1)) as datefield

from test) as Field1,

(select Max(Substring(field, CHARINDEX(' ', field) + 1, CHARINDEX('.', field) - 1)) as datefield

from test

where Substring(field, CHARINDEX(' ', field) + 1, CHARINDEX('.', field) - 1)

not in (select Max(Substring(field, CHARINDEX(' ', field) + 1, CHARINDEX('.', field) - 1))

from test)) as field2,

DateDiff(mi, (select Max(Substring(field, CHARINDEX(' ', field) + 1, CHARINDEX('.', field) - 1)) as datefield

from test),

(select Max(Substring(field, CHARINDEX(' ', field) + 1, CHARINDEX('.', field) - 1)) as datefield

from test

where Substring(field, CHARINDEX(' ', field) + 1, CHARINDEX('.', field) - 1)

not in (select Max(Substring(field, CHARINDEX(' ', field) + 1, CHARINDEX('.', field) - 1))

from test)))