LOL Yep I remembered that
The Eldorans (Raijin-Oh, Ganbarugar and Gosaurer) are the best known for that kind of transformation exaggerations (they have VERY long and extravagant sequences... hell, Gosaurer had dinosaurs and volcanoes in its scenes O_O ), however, they also explicitly show that when you take away all that flash the actual transformation itself takes no less than a few seconds, sometimes even less.
There are still mecha out there that do transform in "real time", but they typically have excuses to do so (GaoGaiGar and Gravion to name two, they create shields around themselves before they combine), and some just leave it to handwaving, as in the case of the Nagahama trio (Combattler V, Voltes V and Daimos).
Strangely enough, Nanoha is shown surrounded by a pink sphere when she transformed in A's ep1 and subsequently destroyed by Vita O_o Nanoha has G-Field? :P