If you're looking at what I wrote (above) and wondering what maths I used the logic was as follows:
1 hour = 15°.
The range of declinations = 90°+90°- your latitude (which I assumed to be 30° roughly) = 150°.
So, if more than 10 objects in a group the dec movements will be <15° on average.
hmmm... you could probably also argue that the average movement in RA will not be 1 hour (15°) but probably 7.5°, so maybe we could allow 20 objects in a 1 hour RA group and 40 in a 1/2 hour RA group
.
But anyway, it should get you started, and you could do it in Excel...
Al.