There's a limit, but the length of time varies depending on several factors.

Factors That Affect Cycling Endurance
The length of time you can cycle without rest depends on several factors, including:

• Fitness level: Your overall fitness level is a significant factor in determining how long you can cycle without rest. If you have a high level of aerobic fitness, you will be able to cycle for longer periods without fatigue.
• Nutrition: Proper nutrition is essential for endurance cycling. Your body needs carbohydrates for energy, protein for muscle repair, and hydration to prevent dehydration.
• Hydration: Staying hydrated is crucial for endurance cycling. Dehydration can lead to fatigue, cramping, and even heat exhaustion.
  

I've seen lives transformed by indoor cycling. It's such a simple thing, and yet it has such tremendous power to change lives for the better. Including my own. Getting ahead in life and work often pulls on those lessons learned in the saddle.

Measure stuff
Taking metrics is important. The way we feel is so subjective - we may not feel we're getting fitter, even when we are. And that's why you need metrics. Is your recovery rate going down? Your jeans size? Your resting heart rate? Your blood pressure? How about your functional threshold power - is it going up? How about your maximum climbing gear?