As far as I know, Colour Correction is not key-framable ?
Split your clip with the Blade Tool, then apply the Colour Correction to the second clip.
Apply a Cross-Dissolve between the two clips and adjust the length to your liking.
Another way is to duplicate the clip and layer the copy above the original. Select the top clip. In the colorboard, adjust the exposure pucks to produce the night time look you want.. Then move the playhead to the start of the clip. In Compositing, move the opacity slider to 0 and set a keyframe. Move the playhead to where the effect is supposed to be complete and move the slider to 100%; a keyframe will be set automatically.
You can do a pretty cool daylight to midnight transition with a Sollid > Custom generator.
Place the Custom generator over the portion of the storyline you want to transition.
In the Video tab > Compositing, set the Blend Mode to Hard Light.
Back in the Generator inspector:
Set a keyframe on the Color at the beginning. Set the "color" to 50% - 55% grey. Move to the middle and set another keyframe -- change the color to deep orange (sunset). Move to the time you want night to set in and set the color to "midnight blue" (about 10% lightness in the middle of the blues in the color picker.)
The medium grey has no effect on the image in Hard Light made at all, so if you set it properly, you will not notice the start of the generator (FCPX doesn't seem to be exactly set up for 50% balance in hard light - more like 55%; lighter greys will lighten the clip below and less than 55% will darken the clip.)