The only importance of the "time" it takes to cause the reaction/sensing is whether it causes a delay or otherwise impacts the time it takes to get to the next shot. With a digital SLR you can take another shot immediately, with film, you either have to manually advance to the next frame or wait for an automatic motor winder to advance the frame for you. Consumer automatic 35mm cameras were insanely slow. And even the highest end motor winders and extra battery packs (for cameras with built-in motors, were considerably slower than the quick DSLRs of today. Some of them are of course able to beat some consumer DSLRS of today, but dollar for dollar, DSLR frame capture is just all-around so much faster.