You can set your store's default lead time. This lead time will show on your product pages as a default. You can always over-write it on your product edit pages.
To set your preferences go to your 'Store' settings page and scroll to 'Lead Time': https://merchantshowroom.com/vendor-dashboard/settings/store/ .
Once you set the 'Lead Time' on your 'Store' settings page, when you create a product, this setting will automatically show on all newly created products. You can always over-write it by selecting another option when you create or edit your product.
This lead time will show on your store's page in the marketplace and buyers will be able to filter results based on the lead time that is acceptable for them. For this reason, it is best to have the shortest amount of lead time possible.