Convert Seconds output to HH:MM:SS Format

[itsmevic]

I'd like to convert the output of the below SPL to reflect HH:MM:SS rather than just seconds.  Any help is greatly appreciated! 

index=* host=* user="username" sourcetype="WinEventLog:Security" EventCode="4624" OR EventCode=4634
| transaction user maxevents=2 startswith="EventCode=4624" endswith="EventCode=4634" maxspan=-1
| eval Logontime=if(EventCode="4624",_time,null())
| eval Logofftime=Logontime+duration
| convert ctime(Logontime) as Logontime
| convert ctime(Logofftime) as Logofftime
| table host, src_nt_host, user, Logontime, Logofftime, duration
| sort user, host, -duration
| rename duration AS "Duration (seconds)"

[renjith_nair]

Try

|eval hh_mm_ss=tostring(duration,"duration")