In Jain tradition, Bij tithi generally means the second lunar day of a fortnight. It is not a universally fixed major religious observance day in Jain Dharma.

That said:

• Some specific regional or temple traditions may associate certain puja, fasts, or vows with a Bij tithi.
• But there is no single compulsory Jain observance that is commonly prescribed for all Jains simply because it is Bij tithi.
• More widely observed Jain sacred days are usually Ashtami, Chaturdashi, Panchami, Dasami, Purnima, and major festival days like Paryushan, Das Lakshan, Mahavir Janma Kalyanak, and Siddhashila-related observances.

So, in short: Bij tithi may be spiritually respected, but it is not generally known as a major universal observance day in Jainism.