Responding to your last two posts. Adding the new substrate gravel would not in itself cause ammonia to rise, but the removal of the former stones a day before would have removed bacteria on the stones, so in effect there was then insufficient bacteria to handle the ammonia being produced by the pleco; in a larger tank this has less effect because of the larger surface area elsewhere for bacteria, but in a 10g the removal of the substrat is significant, plus you recently replaced the filter media if memory serves me correctly, so more bacteria lost. I thnk this explains your ammonia rise today. And the subsequent nitrite rise is the second phase of the nitrogen cycle catching up.
Ammonia at .25 is not so bad with a pH of 7.4 (compared to the former 8.4). I would leave the tank, no further water change at this point. I would add another capful of Cycle (I think they recomend one capful to 10 gallons?). Can't hurt, Cycle can't be overdosed, and it is a bit of a jumpstart with bacteria. Test the ammonia later in the day, and the nitrite; monitor what its doing. You've now added the two snails which will increase the ammonia a bit, but I still say this is not going to harm the pleco. But I would aim for stability, so no further water changes unless it becomes necessary.
Water conditioners work instantly. I squirt some in when I start to fill the tank (I use a Python hose attached to the faucet and fill directly from the tap) and have never had any problems.