This cheat will help you make the most of the Incense and Lucky Eggs you do have.
1. Use your Incense or Lucky Egg (or both) as normal.
2. Leave the Pokémon Go app. On either iOS or Android, navigate to your phone's settings.
3. Go into Time and Date and turn off the automatic time and date setting. Then turn back the clock up to 30 minutes, not more.
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.