RE: Fishless cycling using Dr Tim's One & Only live bacterial product
I don't think the extra One and Only you used would cause ammonia all disappear in 25 minutes. It is simply due to there was too little ammonia to begin with.
Double, triple, etc. drop whatever you need to achieve minimal 2ppm. It isn't going to harm anything since it is a fishless cycling. Without reaching at least 2ppm ammonia concentration, it might not be able to keep ammonia/nitrite free once you move your betta there. The goal is to make sure the aquarium can convert enough ammonia daily (more ammonia than the fish can produce). 2ppm ammonia daily is considered lightly stocked, 5~6ppm ammonia daily is for a heavily stocked fish tank. Always aim for higher if you don't want accidental mini cycle later on.
Toward the end of fishless cycling, the nitrate should go up really quick with little to no sign of ammonia and nitrite at the end of each day (before you drop new ammonia). It is a good sign you have nitrite now, but you really need to start dropping at least 2ppm ammonia to let it cycle as quick as possible. With heavy seeding from bacteria products, your cycle should be finished within days. So far I believe the lack of food source (ammonia) is holding back your cycling progress.
Yeah, community tank is fun with more activities and more variety of fish species. A betta tank is also cool. Planted aquarium is troublesome to take care of though, it will also cost extra money for the proper lights, etc. equipments. Research well before you get started.