If you want to implement grouping by day you can use our DateTimeGroupDescription with Step=Day. To have hour grouping you will have to create CustomGroupDescription and override its GroupNameFromItem method. This method returns the group name where the item will be included to. We have implemented a simple solution for your case, you can find it attached and use it for your reference.
Feel free to contact us if you have any problems or concerns.
the Telerik team