You said..."The rest of the clutch are in moist vermiculite in a dark cabinet. I put them there when she laid them last June. The temp is about 72 degrees"...there is some good information about incubation on this site that might be useful to you....
http://adcham.com/html/taxonomy/species/fpardalis.html
You said..."The rest of the clutch seems to be healthy"...glad to hear that.
You said..."It seems like they take forever between hatchings"...are your eggs close together or spread apart a bit?
You said..."My veiled clutch hatched on after the other like clockwork with great success"...again, were the eggs close together or spread apart a little?
You asked..."Is this gap normal for panthers?"...generally when the eggs are close together, they all hatch at about the same time. When there is space between them, they hatch more individually over a few days or even a month. Also, different areas of the incubation container could be warmer or cooler than other areas so the hatch could be quicker for some and slower for others.