Hello Pedro. Please select your national colors in your profile.
A fruit fly culture is good for about one month on average but the hatching cycle in the culture will ebb and flood. In other words you want more than one culture going at a time so that when one is low on flies and waiting for another big hatch you can use the other one. Springtails (woodlice) are extremely easy to culture and relatively maintenance free to keep.

Good luck and welcome to FrogForum