Localized resources take quite a bit of time to restock. For some highly sought-after resources like pit clay, perhaps it would make sense to have them restock some set amount after a minuimum wait time? e.g. they take 2 weeks to restock 5 clay, then each week after +1 clay up to a maximum of 20.
Or just have them restock 1 clay per day after the 2-week waiting period.