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