Bhadra Tap is typically observed for 3 days.

In this short fasting (tap) you usually:

• take only boiled water during the daytime (sunrise to sunset)
• avoid solid food
• perform usual Jain practices like Pratikraman, Swadhyaya, and Samayik

Some traditions may vary in details or in extending the period for very advanced practitioners, but the common form taught is a 3-day fast. For more on the basic how-to, you can read here .