One of the most important things in either rimfire or centerfire benchrest accuracy is the consistency of ignition. That means a strong, consistent, but not necessarily quick firing pin fall. It's probably more important to rimfire benchrest shooting, due to the priming method and variations in rim thickness, case metallurgy, and headspace variations.
For both venues, the rifle is sitting on a solid rest, both front and rear, so movement is not an issue. Conditions for the shot shouldn't change enough to make a difference between milliseconds of travel. It should be noted that rimfire rifles begin to move in recoil before bullets leave the barrel, due to the relatively slow velocity. Centerfire rifles don't tend to move much before the bullet leaves.
That said, position shooting requires the fastest lock time, to minimize the (continual) user-induced rifle movement after the sear breaks. Nobody can hold a rifle perfectly steady in any non-rested position. If the rifle is moving when benchrest shooting, it's usually a shooter technique problem instead of rifle and/or rest.
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