Dreams depend on your REM cycles (Rapid Eye Movement), this is the stage where you dream. The first REM cycle lasts only a short time, and then you repeat the earlier stages of sleep until you reach another REM cycle. Each time this happens the REM period gets longer, this will be why you got a long dream at 10 The REM cycle would have been longer than the one around 6:30. That's why people who try to WILD sleep for a few hours first, so they can go straight into a REM period, it's much easier.

Hope you're making progress