Five fish probably added a fair bit of ammonia compared to the flakes previously, and the bacteria need time to catch up. Keep the ammonia below .25 with partial water changes of 50%, as needed even if daily. Same if nitrite should appear.
Another thing to be aware of, is ammonia in the source (tap) water. You should test your tap water for ammonia, nitrite and nitrate just to know if any are present. If they are, they can be handled at water changes through a water conditioner that detoxifies whichever is present. Several conditioners will handle ammonia, to my knowledge only Prime also handles nitrite and nitrate.
Also, be aware that these conditioners detoxify ammonia by changing it to the harmless ammonium. A test kit will read ammonia and ammonium the same, as ammonia.
Nitrosomonas bacteria requires about 9 hours to multiply (by binary division, where one bacterium divides into two bacteria) in optimum conditions (meaning, basic pH above 7, and tropical temperatures around 78F). Nitrospira requires longer, around 20 hours, to multiply. Five (presumably smallish) fish in a 50g should not pose too great a problem.