>Have two copies of a property table that I want to sync into a single table. I would on the property application at home, and my friend works on it at their home. We are both adding different properties and possibly modifing the same existing properties. We are not adding the same property.
>
>Guess I should change add_dt and mod_dt to include the time. Any matching key where the add_ts is different, then it is a different property. For any matching key where the add_ts is the same but the mod_ts is different, then is is a modification. Once i have a different add, I can renumber the key and replace. If it is a different modification, I will save the most recent modified date/time. Does this seem correct? Is there something that is more precise than date/time?

For the two of you, datetime should work fine. Though it works only to the seconds level - internally, it stores milliseconds, but you can't get to them. You may get more precision by storing date in a date field and seconds() in a n(10,3) field - that would give you precision to the millisecond.