Since there are more languages and language families in
Africa than anywhere else, I may be being too cynical, but the most common east African languages have nothing like that for "day". "Day" is siku in Swahili, usuku in Zulu and Xhosa. N'dea "sounds like" "(the) day of", so let's be generous and say they misheard. According to
A comparative study of the Bantu and semi-Bantu languages by Sir
Harry Hamilton Johnston however, N'dea is the Taveta (the text has Taveita so the spelling is suspect, but it's a Bantu language of
Kenya) word for Giraffe and so is related to Swahili Twiga, giraffe.