If Medikinet 20 mg works for you, but is too short, you should talk to your doctor and talk about other ADHD treatment options that may provide a longer effect.
The GdziePoLek.pl service also allows you to book the medicine at a selected stationary pharmacy and collect it after presenting a prescription: https://www.gdziepolek.pl/produkty/47472/medikinet-20-mg-tabletki/apteki

There is Medikinet CR, in the form of modified-release capsules. It will ensure a longer effect of the drug, even up to 8-12 hours. https://www.gdziepolek.pl/produkty/47475/medikinet-cr-20-mg-kapsulki-o-zmodyfikowanym-uwalnianiu/apteki

You may also want to check out other medications in other forms, such as Concerta (in the form of extended-release tablets). Your doctor may consider making a change. https://www.gdziepolek.pl/produkty/19569/concerta-tabletki-o-przedluzonym-uwalnianiu/apteki

Please remember to always consult your doctor before changing or adjusting your treatment. Your doctor can adjust the dose or type of medication to find the best solution for your needs. If you do not have the opportunity to consult your doctor, you can use the teleconsultation here: https://www.gdziepolek.pl/telekonsultacja/z-psychiatra