Viewers of ads are from different time zones may be varying in no at large and Clixsense follow EST so my question

No, they're published when they're published, and that's it.

It would be technically easy to add such a feature, but it might not be such a good idea...imagine an advertiser who purchases a million hits, but orders them to only show up at a time of day when a dozen people are logged in on average, so I don't know if it's a good idea or not.

But hit/clicks I mean the traffic of site visit vary during the morning afternoon evening night etc.The advertiser may like to have the attention of certain target groups.So can't the idea of option not considered?

You can stop/pause the ad.

You can also submit a support ticket first and let them know you want to purchase
an ad pack and you want it to begin at such and such time. They may do that for you.

Yeah I totally agree.But perceiving from the angle of
1.Adveriser
2.Members
3.Clixsense
4Visitors
The interests are different and if all the interests can be achieved it will be an wonderful idea

A Win Win situation can be eventualized if
24hrs can be grouped into 5/6 slots for the purpose of ADs as Heavy traffic, Prime time, Lean traffic Normal traffic etc based on the stats readily available.
The advertisers may consider buying slots as per their study and targeted group
The Clixsense can have differential rates and thereby earn more not only revenues but more membership as well more traffic too.
The additional revenue earned can be partially passed on to the members CLICKS which will silence the murmerring of many members regarding the low clicks and lower revenue.
However let us all realise that Ad clicks alone can't be a source of income to break even ones time spent,internet charges, electricity etc.Have to consider doing tasks,offers,surveys etc.