Question:
If it is Erev Rosh Chodesh and you davened Mariv right after Plag , can you still eat meat until sunset.
Please provide sources
Answer:
No. According to the Ashkenazi minhag of not eating meat from Rosh Chodesh, as soon as you davened maariv, the nine days starts.
Best wishes
Sources:
Magen Avrohom 551-26 quoted in M:B 551-56.