Going away during fishless cycle

Without heavy seeding, typical fishless cycling can take up to 6~8 weeks to finish.
It could take more than 3 weeks just to see the first sign of nitrite. If your trip takes place before the appearing of nitrite, there is no need for any extra source of ammonia. Although ammonia might decrease slightly when it is released into the atmosphere, there will always be ammonia in the water until all of them are converted into nitrite.

How long ago did you start the cycling?