You should get the tranny up to temp. The engine will get to temp far sooner. Even the engine oil isn't to temp when the coolant gauge first indicates 85*C or whatever is normal for your engine. Dr. Booth said to go for a 20 mile highway run. My rule of thumb is the tip of the dipstick should be too hot to keep your fingers on when the the fluid is at temp.

Sixto
87 300D