Can I make a transfer between separate airlines in Beijing Capital Airport within 24 hours?

Hi,

We have bought a multi-city ticket from Air China leaving from London to Tokyo and have return flights from Osaka to Beijing on 19th with stop-over for 5days and final return from Beijing to London on 24th. Initial plan is to get a tourist visa and spend 5days in China. However, if we cannot get a visa, I would have to return to London on 19th, but changing Air China ticket will cost me more than original ticket price. Therefore, I’m considering to buy another flight ticket for 19th from a different company (like Ukrainian air). Would it be possible to make that transfer if they are not connected flights (i.e. Osaka-Beijing will be Air China, but Beijing-London will will be another airline company)? Anything else we should keep in mind?

Thanks a lot!