Was the Temple still in operation when Pentecost took place in Acts 2?
Yes. At Pentecost in Acts 2, the Temple was still in operation. No one had told these Jewish believers or anyone else to cast aside Temple worship or the Law. These Jews were still practicing the seven feast days, and Pentecost was the fiftieth day after Passover.
Les teaches that Acts 2 must be kept in its setting: Christ was crucified at Passover, then appeared for 40 days in His post-resurrection ministry, and the disciples waited another ten days until Pentecost, the fiftieth day. He emphasizes that the Temple was still operating, and no one had told these Jewish believers or anyone else to cast aside Temple worship or the Law. These Jews were still practicing the seven feast days, and Jews from the whole then-known world came to Jerusalem for them. So Pentecost took place while Temple worship and Law observance continued.