Bhadra Tap is commonly observed for 3 days. However, in practice some Jains extend it to longer forms (for example, Athai or eight days, or other extended sequences) depending on one’s capacity and guidance from a guru. The core idea is disciplined fasting and spiritual practice during the Bhadrapada period, with Pratikraman, Samayik, and vows of non-violence and restraint. There can be small variations between Digambar and Shvetambar traditions, but the general concept remains the same: a short, focused tap commonly taught as a starting form, with possible longer versions for those who undertake them under proper guidance. You can read more here and here .