but I would think if you can reproduce whatever the conditions were where you found it, that would be best. Ie., keep it in a container that is in an outdoor shed where temps are similar to outdoor temps, maybe with a couple bits of the sort of wood you found it under, or just the bit that it's attached to. Make sure you have it in something secure that tiny things with legs can't get out of. Make sure you check on it regularly. Make sure it doesn't get moldy (from the wood).

I've never raised spiders (if that's what these are). I know there are people here who know more about this than I do. Maybe the outdoor temperature part is not that important? I find it easier to have my galls and acorns in my house so I don't forget about them ... critters have consistently emerged, but who knows what hasn't emerged.

I look forward to hearing about future developments with the eggs. It's great you found the sac again!

If you have spiderlings (or whatever) emerge that you want to raise (maybe they'd be easier to id when larger) hopefully someone here can help with that. I have no idea how easy or hard that is. Or you could photograph them right away and release them back where you found them.

How long do you think it will be before I see something ?

Maybe you should post this question in the forums section so that more people will see it -- I don't know the answer. I'm sure it's partly weather/temperature dependent, and also dependent on the family/species. I would guess it would be between 2 days and 6 months, assuming they are viable. :-) Sorry, not too helpful here...

These guys have still not hatched. It looks like it has changed some though so I'm hopeful.

if you get spiderlings (likely)
try feeding them collembola
but they may also like eating each other

I've been reading up on eggs of all sorts of invertebrates, and I'm confident that these things are all spider egg sacs. The taxonomy has been re-shuffled over the years, but these are hunting (non-web building) spiders of the Clubionidae and related families, including Gnaphosidae.
Sam, I'm not sure if yours has a metallic shine to it or if it looks like that because of the flash, but flat metallic egg sacs are made by Castianeira ant-mimic spiders, which are now placed in the family Corinnidae.

it was due to the flash. It's a web around it and it did have sort of a "sheen" to it but not metallic.

It's possible it is a Sac Spider because I found a spiderling crawling on my jeans here and Lynette thinks it might be a Sac Spider baby. The little one was in the same area as this was. As a matter of fact, I was sitting in the very same spot when I found both of them.

but I've found that unless I actually see them hatch it's not wise to assume they are related just because they are found in the same spot. That being said, I agree that they are spider egg sacs.

did you see Charley's comment above ?

Are you ready to become a foster parent?

not if it's an alien!