Could you please advise the time of last bus from Wulingyuan to Fenghuang?

There are only two direct buses between the two places, one at 08:30 and the other at 14:30. Duration is about 4 hours.

If you want to stay longer in the forest park, you can also take a train later to Jishou (duration is about 2 hours). Upon arrial, walk about 500 yards to the Long-distance Bus Station to take a bus to Fenghuang. The bus operates till 20:30 and ticket fare is no more than CNY25. Duration is about 60 minutes. For the train, you can search the real time schedule on this website.