John Dominic Crossan
Crossan Historical Jesus (352f) notes that this is one of a small group of sayings that express the "opposition, hostility, rejection, and danger involved in accepting either the vision or the mission of Jesus:" 038 Serpents and Doves, 044 Carrying Ones Cross, 054 Dogs and Swine, 063 Saving Ones Life, 072 Fire on Earth, and 081 Strong Ones House. While some of these sayings could have originated within the lifetime of Jesus, Crossan points out that the promised Spirit who will speak in their defence indicates [that there has been a] development from casual opposition to juridical prosecution.
International Q Project
IQP reconstructs the original Q saying as follows:
When they bring you before synagogues, do not be anxious about how or what you are to say;
for the holy Spirit will teach you in that hour ... what you are to say
The commentary in The Five Gospels (p. 110) observes:
The sayings in Mark 13:9-13 all reflect detailed knowledge of events that took place -- or ideas that were current -- after Jesus' death: trial and persecution of Jesus' followers, the call to preach the gospel to all nations, advice to offer spontaneous testimony, and the prediction that families would turn against one another are features of later Christian existence, not of events in Galilee or Jerusalem during Jesus' lifetime.
Ludemann [Jesus] (89) sees this saying as coming from the community after Easter.