It depends on the specific type of culture medium you are preparing and the storage conditions. Some culture media can be used on the same day, while others should be stored before use to ensure their stability and prevent contamination. For a nutritive gelose medium, it is generally recommended to sterilize it before use, which involves heating it to a high temperature for a specific period to kill any bacteria or other contaminants. After sterilization, the medium can be used immediately or stored for a limited period, depending on the particular storage conditions and the stability of the medium. Typically, sterilized culture media should be stored in a clean and sterile container at a cool temperature, such as 4°C, and used within 2-3 days. After this period, preparing a fresh batch of the medium is recommended to ensure optimal growth and viability of the microorganisms.

It is important to follow proper sterile technique when handling the medium and monitor the pH and other parameters to ensure that it remains suitable for use.