Time-turners

[Zarleycat at aol.com]

No: HPFGUIDX 20429

I writing this sort of spur-of-the-moment, so it's probably not very 
well thought out.  

What are the limitations on time-turners?  How far back in time can 
one go?  Can anyone go back to any time, or does the time traveller 
have to be going back to a previous time in their own life?

If there is no limitation, and anyone could travel back in time, 
could the time-turner be used to see just who was at the Potters 
house the night they died?  Could an objective witness go back to the 
street that Peter Pettigrew supposedly died on and take a look to see 
that it was Peter who blew up the street and killed the 12 Muggles, 
and not Sirius?  Could Sirius travel back, again with a witness that 
the MOM would believe, and observe the moment when it was agreed that 
Peter would be the Secret Keeper?

I suppose the quick plot answer would be that there is a time 
limitation and you could not spin it 30,000 times to go back 10+ 
years (no attempt on my part to do the math - if you want to, have 
fun).  

Any thoughts?