That tab has nothing to do with the firing pin block. The safety lever disengages the firing pin block. The tab that you were pushing down on, when the slide is out of battery, gets pushed down by a lack of that milled bit that I mentioned before, preventing the gun from firing when out of battery. Really. Pull your slide off and have a look. While you've got the slide off, pull out the trigger bar. See that small vertical tab just forward of the DA ramp? That's what engages the "tab" on the sear, which disengages the sear from the SA notch on the hammer, allowing the hammer to fall. SA reset is determined by this engagement alone, between trigger bar and sear, so tell me, how does pushing the trigger bar vertically down shorten the engagement?
To look at it another way, you see the way the (larger) tab rides on the inside of the slide? You pushing it down with your finger is EXACTLY what the slide does when it cycles. Pull off the right grip panel and watch it happen. There is ZERO difference in the reset you just experienced and the reset you experience while firing.
If you still insist that it's shorter:
https://www.officialenzyte.com/