Short answer

• The phrase you heard is “kroḍa‑kroḍī” (crore‑crore) years of deva‑gati. Some later Jain granthas and pravachans use such very large numbers to praise the phala of Paushadh because, for a day, a śrāvaka actually lives like a muni. It is an emphatic way of saying “extremely long celestial lifespan,” not a fixed guarantee for everyone.
• Tivihār and Chauvihār Upvās are important tapas, but they mainly regulate intake (food/water). The śāstras generally do not attach a standard, quantified “so‑many‑years in heaven” to each fasting subtype. Their fruit depends on samyak‑bhāva, careful ahiṃsā, and purity, so the result varies widely.

Why Paushadh is singled out

• In both traditions, Paushadh = one adopts several muni‑vratas for the whole day (śīl, saṃyama, svādhyāy, pratikramaṇ, brahmacarya, alpa‑bhoga, etc.). Because it closely imitates monk‑conduct, its punya is described as very weighty, hence the hyper‑large numbers in some texts/kathās to convey “immense merit.”
• Tivihār/Chauvihār regulate “when/what to drink or eat.” They are tapas inside lay‑conduct, not full adoption of muni‑maryādā for the day. Therefore, traditional literature praises them but usually without assigning a fixed numerical lifespan.

Digambar and Śvetāmbara notes

• Śvetāmbara: Posadha is recommended in Āgamic tradition; fruits are described in laudatory terms; emphasis remains on right intent and careful observance rather than a fixed numeric reward.
• Digambar: Ratnakaraṇḍa Śrāvakācāra–type literature extols Paushadh as near‑muni life; again, praise is qualitative/immense rather than a uniform number for all.

Essence to keep

• Do not chase numbers. In Jain Dharma, the dravya‑bhāva (internal purity, kashāya‑kṣaya, and observance without pride) decides the fruit. Paushadh is exalted because it most reduces new karma and burns old karma by approximating muni‑dharma. Tivihār/Chauvihār Upvās are powerful means toward the same end, but their results are not standardized as “X years of deva‑āyu.”

For simple clarifications on these practices:

• Tivihār vs Chauvihār Upvās
• “Tivihār Upvās” pachkhan basics
• “Upvās” pachkhan basics
• Paushadh related achar/dosh (overview)