There is one clock that shows the right time so we do not have to worry about the one which is always correct.
Talking about the second clock that loses a minutes in every 24 hours (or in a day), so after 60 days (since it has lost 60 minutes because it is losing 1 minute everyday) it will show 11:00 a.m when it is exactly the noon.
So this way, in total it will take days before it shows the correct noon.
Now, the third clock gains a minute every 24 hours (or in a day) , after 60 days (when it has gained 60 minutes or a complete hour) it will show 1:00 p.m when it is exactly the noon.
This way, it will take days (since it has gained a minute everyday) when it shows the correct noon.
Therefore, it will take 1440 days before all the three clocks show the correct time again.