Both cases are just a time-speed-distance calculation. Longer distance = more travel time. The ball isn't traveling slower, it just has farther to travel. Timing obviously changes depending on variables like stride length and ball speed.
For simplicity, let's make a few assumptions:
Your pitcher moving from 40' to 43' has a pretty consistent fastball of 55 mph. She has a decent stride, so let's use a measured ball travel to hitting zone distance of "Pitching distance minus 4 feet". (Release point 3' from pitcher's plate, and contact zone 1' in front of rear tip of home plate)
Convert and round, 55 mph = 80.667 feet per second (fps)
Using the formula: Time = Distance / Speed
43' (actual ball travel distance is 39') = 39' / 80.667 fps = .483 seconds
40' (actual ball travel distance is 36') = 36' / 80.667 fps = .446 seconds
The younger pitcher moving from 35' to 40' has an "age appropriate" 50 mph fastball. Her stride is a little shorter, so let's assume "Pitching distance minus 3 feet" for her.
Rounding, 50 mph = 73.333 feet per second (fps)
Again, using the formula: Time = Distance / Speed
40' (actual ball travel distance is 37') = 37' / 80.667 fps = .459 seconds
36' (actual ball travel distance is 33') = 33' / 80.667 fps = .409 seconds
Granted, I'm being pretty generous giving 50 mph to a kid throwing from 36'. I don't think that is typical; speed is probably more like in the upper 40's. But I think there are big gains in velocity at that age, because it's usually when the pitcher starts getting quality instruction and you see a large jump in performance.
Any way you slice it, you're still looking at between .44 seconds and .49 seconds in terms of timing from release point to hitting zone up through 14u travel ball. College typically will bring that timing down somewhat to about the .43 to .45 range for a fastball.
IMO, deceptive change of speeds is the most effective weapon for a pitcher. Do the math for the DIFFERENCE in speeds - say a 60 mph fastball followed by a 49 mph change-up; you'll see why it messes with a batter's timing. That's also my case for a college pitcher needing 60 mph to make the change-up more effective.