So you have many records and you want to see only pairs of rows created in less than 3 sec time window, right?

Are talking about a form of soft realtime? Please try to explain why is 3s limit so important for you, maybe it would be much easier to help you.

select isnull(Fran,'')+' '+isnull(Till,'') as 'Fran Till', Kejdanummer
from kabel
order by kejdanummer