In grocery there are two questions regarding expiration.
On the Vital Info tab:
and on the More Details tab:
If the ‘Is Product Expirable’ value is Yes or True, then the Type will be required.
One of the Type options is shelf life when creating the listing. It is not showing me options on edit, but maybe it will allow you to write it in?
I don’t know if changes to these settings will hold, never tried it.
I use the sku method to track dates. Each new date gets a new sku that has the date in it so I can monitor the time left. If I have 2 skus for the same product and an older sku is getting close I drop the price on that one to get them sold first.