Thank for your help.
but I still have some confuse about the relative time span.
Simplely.I want my event start at 16:00 and close at 16:20
SO,i set the
event Date time:16:21
close time before:1 min(at this time user can't sign any more)
finish Display:5 min(the this event will not display after 16:25)

Is it clear.

Will it have some change at next version,just have tow Date-Time funtion.
just start and end Date Time.

Thank