Jan,
at one point I thought i could 'tell' (the eggs seem to get rounder, the egg casing more clear/thin looking, and you can see the little guys wiggling around inside, and make out their chromatophores rather clearly) but then a set that Camryn Petersen was watching over in Hood Canal hatched, which from the pictures and duration seemed "not done yet", an obviously incorrect deduction on my part.
Best thing to do is just start visiting them a few times a week or set up a schedule with some other dives who are willing to team up, shoot a couple pictures and cycle visits. When we were watching a few nests over the course of a year we visited a weekly for 6 or so months and then logged 60 dives in the last 2 months specifically visiting the same nests, monitoring for the hatch and documenting the eggs/health of the mom. We did this for a few years running and the variability and dynamics we observed were amazing. One mom died really early, and her nest got ransacked by another octopus who proceeded to tear out all the first eggs and then lay her own batch. Another time we actually watched the octopus mate, and then the den got over-run by seastars. The mom didn't lay and didn't lay and didn't lay (she had distinctive scarring on her head so pretty sure it was the same female) and then when all the seastars cleared out (like a month and a half or two months later) voila! whole nest of eggs almost overnight.
I've heard that the water quality and conditions cause a lot of variability in the egg casing and that the time from laying to hatch can also vary (I'd originally been told 150 days to 12 months, and observation from nest being constructed/eggs laid to hatch seemed to put some of ours in the 9-10 month range but it was a cool summer that year) Roland Anderson's book and myriad of articles contain a wealth of information. I also have no idea how the female holding the eggs 'inside' (if her den isn't safe or conditions are bad) impact overall gestation time. Here is a pretty good summary, you can see in this article that Roland's work is cited again and again
http://animaldiversity.ummz.umich.edu/a ... _dofleini/
So basically, in short, I don't know.
![:) :)](./images/smilies/smile.gif)
(beautiful shot though should be an amazing hatch if you can catch it... If i come diving with you will you take me there?)