I've not let one time out yet, but I hate to do things just because a timer says I need to. Also there are some I don't have the skill do do yet which will time out before I get them.
Question: if they time out can I find the leads again?
Yes they do, regardless if you excavate them or if they timed out.
On the other hand, you have 30 days before a lead expires. Don't want to tell you how to play the game, but there are some guides that explain how to level your excavation in a few days.
Thanks. tbh it's not something I've found very interesting really. I only look for the motifs. That said I'll take a look at the guide, if it only takes a couple of day.