Hello,
If the eggs are not fertile they will not hatch. Additionally, the type of skink will change the length of time it takes to hatch. Some skink eggs hatch within days. Some just over a month (40 days) and others several months.
If you can provide more information on the type of skink it is, I could give you a better estimation of time otherwise, the longest time is 4 months I believe.
Thanks,Amy
Certified Veterinary Technician
10 years in animal field, 5 years working as a Vet Tech, pet owner