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No need to wait if you take the control command out of the equation..

By simply unplugging the "in "vac line to the SOV behind the booster and plugging the out line [ green to tranny] into that line, the car should delay shift regardless of temp or computer mapping inputs You have simply brought straigt vac to the tranny shift delay actuator manually.
If it delays then , it is an electrical control problem [ SOV, ECU, CT, etc]
If it doesn't delay, the element/actuator is suspect [ and more probable..]
This is a good diagnostic tecniques as it splits the working system at the
electrical/mecanical "sweet spot.".....................