Rhyno,
As you note, those aren't Japanese plums (loquats). They look like Mirabelle plums.
Where are you located?
There are no hard and fast rules on water to fruit ratios. Some people here feel that straight juice is the way to go, and will use upwards of 10#/gallon wine. Others use as little as 2#/gallon. Personally, I like my wines somewhere in the middle, at 4-6#/gallon, and by doing that instead of straight juice I can get a little more wine from a given batch.
Manley is correct, except that if you take a reading on the straight juice and find that the pH is 2.8, you might want to make a water addition. That is probably not too likely, but I'm not sure.
Since you have a hydrometer, strain some of the juice now that it has been on the pectic for 24 hours, and get a SG reading and post back.
Do you have a way to check pH?