It is evident in Harry Potter and the Prisoner of Azkaban that Harry and Hermione used a time turner to save innocent lives.
They were stealthy going through the grounds when they travelled back, as to avoid being seen.
But when Harry uses the patronus charm on the dementors, the other Harry saw him but actually saw a blue translucent deer. After the charm had finished, there was nothing there to see other than a blue light disappearing.
Hermione too was invisible.
Why did they have to avoid being seen when they were invisible in the forest anyway?