Day Trip to the Longji Rice Terraces

Well, one day is a little tight to see all the terraces, for there is a Jinkeng Rice Terrace up Longji and it takes 3-4 hours by foot to get there from Longji.
Longji has 2 sightseeing points and if you only visit these two, one day will be enough.
From Guilin, the fastest and most direct way to get to Longji is to hire a private car. The fare is about CNY500-700 and duration is about 2-2.5 hours.

Oh I see.. Will I be able to reach the two sightseeing points in Longji by public transit?

Yes, but one day is tight to travel by public transport and you may arrive there in the afternoon (3 hours from Guilin to Longsheng county and 2 hours from the county to the scenic area).
If you want to use public transport, you'd better leave two day for that area.