If you are tired of washed out daytime renderings here is a little tip to try:
Just change the Exposure values in the adjust exposure dialog.

For a Daytime Render:

Exposure Value: 12.5
Highlights: 1
Midtones: 0.5
Shadows: 0.2
White Point: 7500
Saturation: 1.7

These may not be perfect for every single rendering but just adjust these values in little increments to suit your style ( best approach is to change one value a time and see if you like the result) After you get a nice image remember to write down the settings used.)

I'm sure most might still want to touch up the image in another program like photoshop. But this will give you a nice "base image to work on".

For a Sunset Rendering:

Exposure Value: 16
Highlights: 1
Midtones: 0.7
Shadows: 2
White Point: 10000
Saturation: 1.4

This one I'm still experimenting with but its getting there..

Please post your setting if you have found any to be good for other times of the day such as dawn or night time

Hope this helps!

EDIT: What is a rendering gallery without the renderings? Here is a before and after to show the effect of the daytime adjustments.