Do i have to wait for the Jammat to end their prayer?

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while i was praying in the Imam Bargah at the time of Zuhar, a woman came to me and said that i am supposed to wait for the Jamat to end the prayer, THEN i can pray my Fardh namaz. is it true that everytime i have to wait or i have to assume that jammat has done their prayers and now i can pray. she also said that if i want to pray on time ill have to join the jammat like behind the men... can anybody confirm me?