a day enough to visit Nikko?

i aim to visit the toshogu shrine, yumoto onsen , lake chuzenji and the kegon falls, enough?
What time should i start to leave from tokyo?

Buses in nikko usually end at what time?

i aim to visit the toshogu shrine, yumoto onsen , lake chuzenji and the kegon falls, enough?

It is possible if you start early and travel at a medium to fast pace.

What time should i start to leave from tokyo?

The earlier the better.

Buses in nikko usually end at what time?

Around 8pm, but sunset is before that, and there is nothing to do after sunset:
http://www.tobu-bus.com/pc/images/data/20110426160944.pdf

The timing of sunset in Nikko is similar to that in Tokyo:
http://www.timeanddate.com/worldclock/astronomy.html?n=248

You have to walk faster (for toshogu shrine , it s big and u need to walk to it and surrounding it is some other interesting temples/shrines)....i did about 75% of what you stated....
But as night falls, the bus frequency is lower, and if you missed one bus,you can camp at the nature site then.......You have to include meals/breaks, photo-taking in between too