It will take a bit of trial and error to work the time out.
Are you going to be direct hot charging?
What will you hot reduction be before you do any cold work?
Often people cheat on the slab homogenization and count on the hot work to finish the job.
But this can be problematic depending on the degree of segregation.
by M9, do you mean 9 metric tons, so it is static casted (vs continuously cast)? if this is the case, the solidification will be slow, and hom process is almost a must to eliminate cast segregation. Hom could also dissolve ferrite for this alloy because Si is a ferrite former.
caution to be taken do not hold too long time to avoid sulfur and oxygen impurities rejected from austenite and diffused to grain boundaries, where they form weak, plastic films that can degrade hot workability. Grain growth worsens this effect.
Uniformity is critical.
Go to about 20C below the max hot work temperature in the spec sheet.
Soak long enough to assure that the entire slab is as uniform as possible.
If you furnace has +/-25C variation it will limit your hot reduction because of the difference in workability.
Be very careful to not go clear to the minimum hot work temperature.
The ductility drops off very fast.
