How much time should a startup ceo devote to reading?

There is no formula for that. Read as you need to. Have your mentor(s) suggest books that are specific to your needs. A good starting point might be one relevant book per month to start. There are also those book summary services that can give you the themes of the books in 5 minutes of reading. Subscribe to that and then you can get the full versions of the books you connect with best.

You should be reading all of the time. The common trait all successful individuals have is a thirst for knowledge.

If you don't have that thirst, you should probably not try to start your own company.

The right question here really is to ask what you should be reading. Once you figure that out, you can plan how much time you want to spend on it given all of your other responsibilities as a startup CEO.

These days, it is very easy to spend an entire day reading interesting things without getting anything useful done! :-)

P.S. - I myself am a voracious reader, but try hard to practice what I am preaching above.

I will recommend you the 5-Hour Rule. During his five-year study of more than 200 self-made millionaires, Thomas Corley found that they do not watch TV. Instead, an impressive 86 percent claimed they read — but not just for fun. What is more, 63 percent indicated they listened to audiobooks during their morning commute.
Productivity expert Choncé Maddox writes, “It’s no secret that successful people read. The average millionaire is said to read two or more books per month.” As such, she suggests everyone “read blogs, news sites, fiction and non-fiction during downtime so you can soak in more knowledge.” If you are frequently on the go, listen to audiobooks or podcasts. Maybe you are thinking: Who has the time to sit down and read? Between work and family, it is almost impossible to find free time. As an entrepreneur and a father, I can relate — but only to an extent. After all, if Barack Obama could fit in time to read while in the White House, what excuse do you have? He even credits books to surviving his presidency. President Obama is far from the only leader to credit his success to reading. Bill Gates, Warren Buffett, Oprah Winfrey, Elon Musk, Mark Cuban, and Jack Ma are all voracious readers. As Gates told The New York Times, reading "is one of the chief ways that I learn, and has been since I was a kid."
The five-hour rule was coined by Michael Simmons, founder of Empact, who has written about it widely. The concept is wonderfully simple: No matter how busy successful people are, they always spend at least an hour a day or five hours a work week learning or practicing. And they do this across their entire career. Simmons traces this phenomenon back to Ben Franklin, who was constantly setting aside time to learn. Franklin generally did this in the morning, waking up early to read and write. He established personal goals and tracked his results. In the spirit of today's book clubs, he created a club for artisans and tradesmen; they had come together to pursue self-improvement. He also experimented with his new information and asked reflective questions every morning and evening.
Today’s successful leaders have embraced Franklin's five-hour rule by breaking the rule into three buckets.
1. Read: Self-made millionaires including Mark Cuban and Dan Gilbert, owner of the Cleveland Cavaliers, read between one and three hours daily. Elon Musk learned how to build rockets, which lead to SpaceX, by reading. Besides expanding your knowledge, Jack Ma, co-founder of Alibaba, says that “reading can give you a good head start; this is often what your peers cannot obtain. Compared to others, readers are more likely to know other industries' strategies and tactics.” Even if you cannot commit to an hour or more of reading every day, start with 20 to 30 minutes. I always have a book with me so when I am waiting for a meeting to start or in the waiting room of a doctor’s office, I can read instead of waste time on my smartphone. You could also try audiobooks during your daily commute or when exercising.
2. Reflect: The five-hour rule also includes reflecting and thinking. This could be just staring at the wall or jotting down your thoughts. For example, Spanx founder Sara Blakely is a long time journaled. Focusing on the past gives you a chance to learn from mistakes you have made, as well as assess what you did correctly. As a result, you will be better suited to achieve your goals and improve your life. In 2014, a University of Texas study found that mental rest and reflection improves learning. Need help getting started? Schedule reflection time in your planner. I’ve found blocking out 15 to 20 minutes after lunch is ideal because I’m coming out of that post-lunch slump. But start small: Allocate five or 10 minutes per day, then work your way up so you’re not overwhelmed. Know the questions you want to ask. Stick with just two or three questions focused on that specific day. For example, if you attended a conference, ask, “What were the key takeaways?” and “How can I apply this to my business?”
3. Experiment: The third and final bucket is rapid experimentation. Ben Franklin and Thomas Edison became leading inventors and thinkers because of their experiments. We have Gmail because Google allowed employees to experiment with new ideas. The reason experiments are so useful is because you have facts, not assumptions. Experiments show you what is working. You can learn from your mistakes and obtain feedback from others. Best of all, experimentation is not that time-consuming. Most of the time, you are testing through the same activities you would perform without testing. Jack Ma even recommends applying the knowledge you have learned to a real-life scenario. For example, after reading a book about collaboration and teamwork, you could take on new volunteer work to put that knowledge to use.
Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath