There will always be customs staff at the airport to take care of travers, no matter what time their plan will land.
There are also taxis available at anytime to take people to theirs hotels.
From my point of view, Goree Island, Pink Lake and a Dakar night Out are the things that someone from abroad must do while in Senegal.
Having said that, I am a professional and english-speaking driver/guide who can help you having a good time in Senegal. It would be a pleasure to best help and guide you while you are in this wonderful country.
If interested, please contact me at: email@example.com
Looking forward to hear from you!