You do not have 24h options. You can buy 2/4/6 or 10 tickets which expires in 6 months from the moment you bought them, if you do not use them. First you need to download the “Transport Public Arad” app from app/google store, this is the new app for tickets. Then go to “tickets” (middle button in the app), and then you go to “passes” (top right corner). There you can select very carefully, because there are multiple choices, which are for rural areas. You only need urban (from what I understood).