Fish timing @ end of cycling

[Stalemate]

Been cycling our first 250 gallon setup for 18 days.   Ammonia and nitrite were zero the other day, but seeing some ammonia again and zero nitrite today.  Is it this naturally possible, or a result of noobing up the tests somewhere along the way?

Hoping to get some consistent tests over the next few days, but it looks like we may be close to the end of the cycling process.  If fish are not added at the correct time during the end of cycling is the cycling process invalidated / ruined? Between indecisiveness on a fish breed* {Tilapia, Bluegill, koi?} and finding a driveable (Baltimore, MD) source.  

I've got some health looking plant sprouts in the grow bed; i'm worried about negative progress e.g. killing them off.

[TCLynx]

What sort of dosing schedule are you using in your fishless cycling?

When you can dose to 1-2 ppm of ammonia and by 24 hours later if you have 0 ppm ammonia and 0 ppm nitrite then you are "fishlessly cycled" If you are not able to get fish immediately once you reach that point, you can simply continue dosing the ammonia to 1 ppm daily to keep your bacteria well fed until a couple days before you can get your fish.  Make sure your ammonia and nitrite are both back to 0 before adding your fish and don't dose any ammonia once you do add fish.

Definitely need plants in if you are regularly dosing with ammonia since otherwise you will have sky high nitrates.

[Stalemate]

We used amonia hydroxide and accidentally over shot the mark initially having >8ppm.   Fast forward to present, it seems to have stabilized.

[TCLynx]

Ok, so your initial dose was super high.

And now your ammonia and nitrite are near 0.  When was your last dose of ammonia and how much did you dose?

When you can dose to between 1-2 ppm of ammonia one day and have both the ammonia and nitrite read 0 ppm 24 hours later then you are cycled up.

Simply dosing high once and waiting however long till both ammonia and nitrite are 0 doesn't necessarily indicate that cycling is complete since if you are not continuing to feed the bacteria ammonia, they will die back off.