If we agree that Mark’s gospel was the first to be written then the following ideas ought to be taken into account

AD 40 the reign of the mad Emperor Caligula Mark 13:14
Generally thought to be too early.
More likely date AD 60 onwards.

Papias recalled a tradition which had been told to him by "the Elder" (ie John) about Mark,
who "having been the interpreter of Peter, wrote down accurately, but not in order all that he remembered of the Lord’s sayings and doings."

Irenaeus (Bishop of Lyon)
States that Mark wrote after the death (exodus)
of Peter and Paul.

Two problems here
1 What is the meaning of exodus?
2 When did they die?

Possibly therefore AD65 onwards.

Josephus the Jewish/Roman historian gives graphic descriptions of the plight
of the Jews in the war against Rome.

V Taylor
Thought Mark wrote in the mid 60's during the persecution of Nero.
The gospel has an interest in suffering, martyrdom etc.

W Marxsen
He decided on a date in the second half of the 60's during the
Roman Jewish war, but the gospel did not know of the fall ofJerusalem.

S G F Brandon
Thought the date of composition was post AD70,
when the certainty about the parousia was beginning to fade. Mark 13:24 & 32.