and, being assembled together with them, he charged them not to depart from Jerusalem, but to wait for the promise of the Father, which, [said he], ye heard from me: (ASV)
Mark 16:8 and Matthew 28:16 both have Jesus instruct the 11 disciples to go into Galilee, whereas this verse claims Jesus ordered them not to leave Jerusalem
The context for Acts 1:4 is--
1 The former account I made, O Theophilus, of all that Jesus began both to do and teach, 2 until the day in which He was taken up,â€¦ 4 And being assembled together with them, He commanded them not to depart from Jerusalem, but to wait for the Promise of the Father,â€¦ 8 â€œâ€¦you shall receive power when the Holy Spirit has come upon you; and you shall be witnesses to Me in Jerusalem, and in all Judea and Samaria, and to the end of the earth.â€ 9 Now when He had spoken these things, while they watched, He was taken up, and a cloud received Him out of their sight. 12 Then they returned to Jerusalem from the mount called Olivet, which is near Jerusalem, a Sabbath dayâ€™s journey. 13 Andâ€¦they went up into the upper room where they were staying:â€¦
This event occurs between the crucifixion of Jesus prior to the Passover and Pentecost. Pentecost occurs 50 days after Passover. The context allows for this event to occur close to Pentecost and perhaps 6-7 weeks after the crucifixion.
In Mark 16, we are told:
1 Now when the Sabbath was past, Mary Magdalene, Mary the mother of James, and Salome bought spices, that they might come and anoint Him. 2 Very early in the morning, on the first day of the week, they came to the tomb whe the sun had risen. 5 And entering the tomb, they saw a young man clothed in a long white robe sitting on the right side; and they were alarmed. 6 But he said to them, â€œDo not be alarmed. You seek Jesus of Nazareth, who was crucified. He is risen! He is not here. See the place where they laid Him. 7 â€œBut go, tell His disciples--and Peter--that He is going before you into Galilee; there you will see Him, as He said to you.â€ 8 So they went out quickly and fled from the tomb, for they trembled and were amazed. And they said nothing to anyone, for they were afraid.
This event occurs immediately after the crucifixion and before the event described in Acts 1.
In Matthew, we are told:
1 Now after the Sabbath, as the first day of the week began to dawn, Mary Magdalene and the other Mary came to see the tomb. 2 And behold, there was a great earthquake; for an angel of the Lord descended from heaven, and came and rolled back the stone from the door, and sat on it. 3 His countenance was like lightning, and his clothing as white as snow. 4 And the guards shook for fear of him, and became like dead men. 5 But the angel answered and said to the women, â€œDo not be afraid, for I know that you seek Jesus who was crucified. 6 â€œHe is not here; for He is risen, as He said. Come, see the place where the Lord lay. 7 â€œAnd go quickly and tell His disciples that He is risen from the dead, and indeed He is going before you into Galilee;â€¦ 9 And as they went to tell His disciples,â€¦ 16 Then the eleven disciples went away into Galilee, to the mountain which Jesus had appointed for them.
Here, it seems that this event also occurs immediately after the crucifixion.
There is no conflict. Matthew and Mark describe an event that occurred immediately after the crucifixion of Jesus. Acts describes an event that occurred several weeks later.
This verse also leaves one wondering how and when the disciples all came back together after fleeing during the arrest and crucifixion.