4. When you re-open the game, you'll see in the upper right-hand corner that the countdown has increased from 30 minutes to up to 60 minutes. It won't work for more than that, so don't set your clock back more than 30 minutes.
The only quibble with the hack — besides that it will probably be fixed soon — is that some are saying despite the appearance of additional time on the screen, your Lucky Egg will still only work for 30 minutes. Meanwhile, many others are reporting that the hack is working just fine for them.
Still, others are saying that the discrepancy is that Lucky Eggs only work for the allotted 30 minutes, but the Incense will keep going beyond the original 30 minutes. That's a little harder to detect since there isn't a set rate at which Incense attracts Pokémon. The swirling purple fog around your character does continue to be present beyond the original 30 minutes, though. Either way, it can't hurt to give it a try and become your neighborhood's Pokémaster.
Just remember to set your clock back to automatic before you go to bed. "I was cheating at Pokémon Go" isn't an excuse most employers understand.