Short answer: “Chunari upwās” is not a fixed, scripture-defined Jain tithi. It is a local sangh/tradition-based shravikā bhakti-upwās/mahotsav (often with chunari-odhān, stavan, and pūjā) that temples usually schedule during Paryushan programs. So its date varies by city and mandir.

Practical guidance for 2025:

• Shwetāmbara Paryushan in 2025 is observed from 20 August to 27 August. Many sanghs keep the Chunari event on one of these days (often around the “Bāḍā Kalpa”/Janma Vachan day). ( timesofindia.indiatimes.com, en.wikipedia.org)
• Digambar Das-Lakshan (post-Paryushan) in many places is 28 August to 6 September 2025; some Digambar sanghs may keep their Chunari-style mahotsav/fast within this period. Please confirm locally. ( amarujala.com)
• Reports from community events show “chunad/chunari” songs and odhān during Paryushan day programs; again, the exact day is set by the local committee. ( bhaskar.com)

What you should do:

• Check your city’s Jain temple/Paryushan schedule or your sangh’s circular for the exact date and pachkhan details.
• If you follow a printed/online Jain panchang, look under your mandir’s “Paryushan daily program”; the “Chunari” upwās day will be listed there.

Essence: It’s a devotional observance organized by the sangh, not a universal calendar tithi.