This works with sql server 2008 too.

create table #dates

(

RecordId int primary key clustered

,RecordDate datetime

);

insert #dates

(RecordId, RecordDate)

values (1, '2015-04-01 14:00'),

(2, '2015-04-03 15:00'),

(3, '2015-04-03 16:05'),

(4, '2015-04-03 19:23'),

(5, '2015-04-06 09:15'),

(6, '2015-04-06 11:30'),

(7, '2015-04-07 12:00'),

(8, '2015-04-09 15:15');

with S as (select *,row_number() over (partition by convert(date,RecordDate) order by RecordId ) as Num from #dates)

select RecordId, RecordDate from S where num=1