Imagine you could schedule a call with serial entrepreneur Mark Cuban or social-media guru Gary Vaynerchuk anytime you need business advice. Two websites, Clarity and LiveNinja, make that possible, letting you pay by the minute to chat with entrepreneurs, consultants, and analysts in a variety of fields. I recently gave the sites a whirl, looking for tips for my son-in-law's start-up and suggestions for sprucing up my blog.

Clarity, which debuted in May 2012, caters to entrepreneurs and features some 11,000 experts. On the site, you can do a keyword search to find experts in specific areas, including bootstrapping and search-engine optimization. Most experts charge about $1.50 a minute, on average. Want advice from Mark Cuban? You'll pay $166.67 a minute for the privilege.

I registered on using my Linked­In account information, then typed startup in the search box. Profiles on about 150 experts popped up, including a headshot, rating, fee, and typical call length for each one. I browsed the list and clicked Request a Call with Lean Startup author Eric Ries, who charged $8.33 a minute. A calendar popped up indicating that Ries was available later that week, and I scheduled a 15-minute call, which he confirmed the next day.

At our scheduled time, I called the dial-in number supplied by Clarity. Ries was about five minutes late, but during our call he gave great advice about how my son-in-law could use early customer feedback to refine his product. The call was well worth the total price of $124.95, which I paid on using a credit card.

Next, I tried out LiveNinja, which launched in December. Not just for business, the site lets you schedule online video chats with more than 500 experts in a range of topics, including yoga and SEO. (LiveNinja plans to roll out an app for mobile video chats this month.) Most experts on the site charge about $1 a minute, but some, including Vaynerchuk, offer free 15-minute sessions.

After registering using my Linked­In information, I typed social in the search box, and profiles on about 100 experts popped up, listing their skills, fees, and ratings. I clicked Book Session to schedule a free chat with Debbie Horovitch, a social-media strategist, the next day. Unfortunately, when I tried to reschedule three hours before the call, she was unable to accommodate me.

So I booked time with Alfonso Martinez Lagares, a Web designer for LiveNinja who charges $25 for 30 minutes. The site requires users to prepay, so I added $50 to my account using a credit card. During our 30-minute video chat on the LiveNinja site, Lagares suggested I optimize photos on my blog so the pages would load more quickly, among other useful tips.

I was impressed with both services, but I would recommend Clarity to business owners looking for advice from other entrepreneurs. Heck, you might even sign up as an expert and start a side business of your own.