Time Turners

[Rhonda]

No: HPFGUIDX 30119

Question:
I have just finished Prisoner of Azkaban and want to know what would 
have really happened if Harry and Hermione had seen their alternate 
selves after turning back time and waiting for Sirius to be 
imprisoned?  The whole outcome depended on them having to have had to 
turn back time in the first place right, because the only way Harry 
defeated the Dementors, was because he was able to conjur a Patronus 
the second time.  The Second Harry knew that he wasn't supposed to 
have been seen or horrible consequences would occur, yet he WAS seen 
by the First Harry who mistook him for his father.  Just because he 
mistook him for his father doesn't have any bearing on the fact that 
he was seen and more importantly realized what happened the second 
time around. Apparently nothing happened with the exception that he 
carried the knowledge from both timelines, so why couldn't Harry have 
turned back time again with Hermoine and thwarted the whole thing 
from get go by giving Scabbers to Crookshanks, saving Buckbeak and 
possibly cleanly clearing Sirius' name, or am I thinking about this 
too much :) ?  Please ignore this thread if it's been brought up 
before.

Help me out.
Rhonda