Data Directly into Grouped Dimension?

Good afternoon,

I was wondering if there is a way to make it so that data goes directly into a grouped dimension? If you have data coming in daily from a database, how do you get it so that instead of going into it's original dimension and you having to update the group constantly, it goes straight into the group?

For example:

Say you have a timestamped field on your server and you want hours 0-12 to go into a grouped dimension called daytime and 13-24 to go into a group called nighttime or something. But instead you just keep getting timestamps coming in and have to manually place them into the group?

I hope that was clear. Thanks!