Yes, First Act Turn = 2nd Story Driver (confusing terms sorry)
I asked a question about this a while ago and expert Mike Wollaeger implied that it's probably okay to have a signpost sort of drag behind until after the relevant driver. (though perhaps not optimal)
Also in this thread there was some disagreement about whether drivers are more focused on the OS or apply to the entire story:
My take is it's probably okay for your IC signpost 1 to drag a bit. Especially if it occurs along WITH the 2nd story driver (even if it's towards the end of that event), you may not have anything to worry about.