I'm going to answer by explaining this and that, as I don't know your particular level of understanding of the nitrification cycle, so pardon me if some of this is old news.
Fish produce a fair bit of ammonia and nitrosomonas bacteria need to be there to use it fast. [Live plants will also use it, even faster. But for the purpose of this answer, we'll assume no plants.] The bacteria take time to appear once ammonia is present, and they take time to multiply; they will multiply so long as there is ammonia for them to use. "Seeding" the tank with bacteria in existing filter media, substrate, wood, rock, decor from an existing tank, or with biological supplements like SafeStart (which is 100% live bacteria) sort of jump-starts the process, so there are bacteria there to handle the ammonia produced by the fish right from the first, and if the fish are few in number and the bacteria sufficient in number, all will be well. These bacteria produce nitrite. Same thing for the second phase, when nitrospira bacteria appear to use the nitrite and change it to nitrate.
If there is insufficient ammonia and/or nitrite for the number of bacterium present, the bacteria will die off as it has no "food". The point here is that with no fish in the tank to produce ammonia, the bacteria added from the "seeding" will die off; this only takes a few hours.
I would suggest you add your 3 guppies and use SafeStart the same time, according to directions on the label. Do not add any more fish until the tank is cycled for the three guppies. Monitor ammonia and nitrite daily, if either goes above .25 ppm do a partial water change of 50% using a good conditioner. When ammonia falls to zero, and then nitrite at zero, for consecutive days, the tank is "cycled" for the 3 guppies. After that point, you can add another fish or two, etc. But a 10g is not large, so be careful on the number of fish.
If ammonia and nitrite remain below .25 ppm, the partial water change can be done once a week, normally.