Another When and Where Question

[EZ1]

When I see the big message "xxxx requesting escort at yyyy in 10 minutes", when does the enemy get to coresponding "xxxx spotted west of yyyyy" message. I would expect that the "xxxx spotted..." message would come up 10 minutes after the "xxxx requesting escort...." message. That doesn't seem to be the case. I can rarely find these formations. Is this something that is completing under the control of the mission builder.