Hakata and Takachiho Gorge

Hi guys! I was planning a day-trip for my Kyushu trip and after researching, I came up with the following plan:

December 2014 period, Thursday

Hakata Bus Terminal to Takachiho Bus Center
Time: 8.03am to 11.35am
Operator: Nishi Nippon Railroad

Takachiho Bus Center to Hakata Bus Terminal
Time: 6.30pm to 9.59pm
Operator: Nishi Nippon Railroad

This leaves myself with approximately 7 hours in between, inclusive of walking to and fro the gorge and the bus center.

Is a total of 7 hours too much time just for the gorge? I'm a fast walker with pretty good stamina, and I do have an alternative choice of taking the 4.30pm return bus instead of 6.30pm.

If traffic jam is known to occur, do let me know as well!

Please advise! Thank you!

Please note that the sunset time in Takachiho in December is around 17:15.

http://www.town-takachiho.jp/culture/tourism/entry091126272.html

In the twilight, I think you can hardly see anything at the countryside like Takachiho.

Oh crap! I totally forgot about the sunset timing. That's me for living in this part of the world where we are summer all year round...

I guess there's no reasons to stay till that time then. Thanks!

That still gives you enough time to see the gorge leisurely, as well as some other places.
The boats can be a bit pricey though. You can see a good video of the gorge at:
https://www.youtube.com/watch?v=H49x41ViFJk
When you get back, you still have some time to enjoy the evening. There is a good list of places to see and things to do for Fukuoka at:
http://www.thejapanfaq.com/fukpic.html