The 24-hour (or 72) visa exemption: both way possible?

We are flying from Germany Frankfurt to Singapore for 2 weeks holiday and both way we have a transit time in Beijing (10 and 24 hours) I have a japanese passport (I am japanese) and he has a german passport (he is german).
Is it possible to go to Beijing city to have a tour in both way with 24/72 hours transit permit exemption ?
26th March (Frankfurt-> Beijing -> Singapore => 10 Hours in Beijing)
8th April (Singapore -> Beijing-> Frankfurt =>24 Hours in Beijing)