Citron & Rose opened in November as an anomaly: a Main Line restaurant closed on Saturday nights.
The Merion Station newcomer, run by Zahav's Steve Cook and Michael Solomonov, follows kosher law and observes the sabbath, which runs sundown Friday to sundown Saturday.
So why not open Saturday night after sundown? The initial thinking was that the kitchen could not work on Saturdays doing prep. Also, observant Jews typically eat their large Saturday meal at lunch, so the idea of C&R's typical dinner meal did not scale.
Starting immediately, though, Citron & Rose is starting an abbreviated menu, motzei shabbat: Mushroom knishes, salmon pastrami crudo, beef tartare, chicken liver parfait, and the like. The bar opens a half-hour after sunset and the dining room an hour after.
Sunset counts as three stars visible in the sky. If it's cloudy, check an atlas.