Hi @Bence Domonkos5CE7, Welcome to our Adobe Express community!! Thanks for reaching out.
Currently, only 12hr time format is available in the scheduler tool for Adobe Express. If you're looking for a 24-hour time format, you can drop a feature suggestion to our product team directly by posting here: https://adobe.ly/4jllq6k
The product team might reach out to you asking for more info on the same.
Best,
Amitej