Answer

For a flight crossing 12 time zones, conduct Chauvihar based on the sunset of the place where you are physically present, not simply by the clock time of your departure or destination.

In practice:

• Take food and water only before the relevant sunset.
• Once you begin Chauvihar, do not take food or water until the next sunrise.
• For air travel, it is safest to start Chauvihar before boarding or before the earliest possible sunset during the journey.
• If there is confusion due to changing time zones, follow the stricter and safer spiritual approach: begin earlier rather than later.

Explanation

Chauvihar means abstaining from all food and water after sunset until sunrise. The main basis is the natural cycle of sunset and sunrise, because Jain conduct gives great importance to avoiding harm to subtle living beings, especially during nighttime.

When flying across many time zones:

• The airplane clock, departure city time, and destination city time may all differ.
• The sun may appear to set or rise at unusual times because the plane is moving rapidly.
• Because of this uncertainty, it is best not to calculate Chauvihar loosely by convenience.

A careful Jain approach would be:

• Before the flight: Eat and drink sufficiently before starting Chauvihar.
• During the flight: Avoid food and water once Chauvihar has begun.
• After landing: Break Chauvihar only after sunrise at the place where you are physically present.

Spiritual Understanding

The purpose of Chauvihar is not only time calculation. It is a discipline of:

• Ahimsa
• Self-restraint
• Awareness of living beings
• Reducing attachment to taste and bodily comfort

So when the exact timing is difficult, choosing the more restrained option preserves the spirit of the vow.

Takeaway

For a flight through 12 time zones, the safest Jain practice is:

Finish food and water before boarding or before the earliest sunset risk, observe Chauvihar throughout the flight, and resume only after sunrise wherever you are physically present.

If this is connected to a formal vow, tapasya, or pratikraman rule, it is best to confirm the exact timing with your Jain Guru, Sadhu-Sadhviji, or knowledgeable local sangh authority.