My personal experience is that if you are a cyclist who needs to get rid of body fat then Keto while cycling is a good weight loss strategy. Your endurance will depend on a lot of factors. How fast your body can draw energy from it's own fat depends on a lot of factors.
If you are a cyclist who doesn't need to get rid of fat, there is no real reason to get into a state of ketosis. There are some studies that suggest enhanced performance during some states of ketosis. It is theorized that it is a survival mechanism from our ancestors that can enhance a starving human hunter for a short period of time enabling them to retain energy and focus enough to hunt down and kill wild game. I would only speculate that to enter that perfect state for a specific time would be so difficult as to make it nearly impossible to utilize for most humans to any degree of advantage.