HI Prithvi,
Not sure what is the version of BO CMC that you're using.
However, here are links to the Administrator's guide for XI 3.1 SP3 and BI 4.0 SP05 (no relevance to the version of the documents provided).
You will find the correct info here:
http://help.sap.com/businessobject/product_guides/boexir4/en/xi4sp5_bip_admin_en.pdf
http://help.sap.com/businessobject/product_guides/boexir31SP3/en/xi31_sp3_bip_admin_en.pdf
For scheduling a report, right click on a report and select schedule.
In recurrence, set the recurrence to "Hourly". Set Hour(N) = 8.
The start and end date will determine for how long (how many days, etc.) will the report schedule generate an instance every 8 hours.
For role assigning I'd recommend having a look at the guides as the procedure involves several steps/options that you could set to tailor your needs.
Hope this helps.
Regards,
-Sid