SQL Server 2012 :: Nested Query Retrieving Min And Max Values?

I have a nested query that retrieves a min value. I would like to know how do i retrieve the corresponding time with that.

my data looks like this

valuevaluetime
1212/31/14 14:51
12.42/19/15 23:30
[highlight=#ffff11]10.92/21/15 6:40[/highlight]
13.21/25/15 20:47

My min value is 10.9 and i need the date 02/21/15

my nested query is as follows

( select min(cast(f.valuestr as float))
from bvfindings f
where f.ObjectName = 'Hematocrit'
and f.sessionid = s.sessionid
and f.ValueTime > s.open_time)

the above returns me the 10.9

i modified the query

select min(cast(f.valuestr as float)),
f.valuetime
from bvfindings f
where f.ObjectName = 'Hb'

but i get all values then.