Green’s Dictionary of Slang

(S.Afr. black) Thursday, the day that most nannies and maids are allowed off work.

[1846		Bell’s Life in Sydney 21 Mar. 3/3: Considering that this was ‘Sheelah’s Day,’ there was little work for the magistrates, if we except an honest Hibernian who was dancing the Polka in Market-street].
[1846		Bell’s Life in Sydney 28 Mar. 1/2: SHEELAH'S DAY.—In the number of appearances before the police court, the Lady Sheelah had the advantage over St. Patrick, as there were two devotees to her influence who were, however, discharged].
1974		Eng. Usage in Southern Afr. V:1 8: In Soweto, Thursday is Sheila-day, day off for the nannies .
1980		M. Melamu ‘Bad Times, Sad Times’ in Mutloatse Forced Landing 51: It’s ‘Sheila’s Day’ Babsy gets a special dispensation [...] to share the privilege of a day off with the Jo’burg domestics.
1989		M. Tlali Footprints in the Quag 40: Why do you think in the ‘whites only’ ‘kitchens’ there is what is known as ‘Sheila’s Day’ and we never hear of ‘John’s Day’? . . . I have never heard of ‘white “Sheila’s Day”’ either.
1996		D. Ndlovu Sheila’s Day in Perkins (1998) 143: Domestic workers both in South Africa and the U.S. got their day off on Thursday. The day, Thursday, is called ‘Sheila’s Day’ in South Africa.
2010		Hartford Courant (CT) 30 July DO1: The show ‘Sheila’s Day’ [...] domestic workers known as ‘Sheilas’ — one [group] in Alabama in the ’50’s and ’60’s and another in Soweto.