Hi Nihar,
I think you're talking about time buckets which is usually configured to decide the bucket strategy to shift the receipts and issues.Similarly, I also see that there is an option for Forecast time bucket settings. Though I do not have practical working experience on this option, I think this would be correlated with the Forecast check that you decide to do against the Planned Independent Requirements ( PIRs ). You need to enable the Check against Forecast in Check Instructions tab. I think this would align the PIRs based on the shift hours that you maintain here.
You may want to take a look at the below post
http://scn.sap.com/thread/3436787
Hope this helps
Babu Kilari