you can do that in many ways, one is below:
query HDS Agent_Event_Detail table for Event = 1 and whatever Date time you are looking for.
event = 1 is for event Login gets recorded table when agent logs in.
you can extract skill target id from the output and actually gets the enterprise name of the agent from that by querying again t_Agent table in AW.
below query will work if you have aw_db and HDS co-located
select EnterpriseName from <aw db instance>.dbo.t_Agent where SkillTargetID in (
Select SkillTargetID from Agent_Event_Detail where Event = '1' and DateTime > '2015-02-24')
the above will give name of all the agents logged in after '2015-02-24'
Chintan