From Heroes Wiki
Future Hiro warns Peter that he may be risking a rift in speaking with him.
"You're talking out of your ass. You don't know how any of this works."
- Hiro expresses his concern in a blog entry that he "might be risking a rift" by going back in time to save Charlie. In another Heroes Evolutions culmination, Hiro sends an email to Hana stating that going back to give Peter Petrelli a message is a rift, but that the "rift is not a risk. It can't be."
- In an interview for Heroes Unmasked, Masi Oka explains that Future Hiro gives the message to Peter as a way to communicate to his past self, presumably to avoid a rift.
Please refer to Theory:Rift for fan-created theories and other speculation.