You may not need an app,
Also see this thread https://community.shopify.com/c/shopify-discussions/how-to-show-expected-arrival-date-in-transfers-to-product-page/td-p/316491
You can quickly leverage the variant.next_incoming_date if :
- it is a single variant product, otherwise you may need a javascript customization.
- using a theme that is online-store 2.0 compatible
- the theme has text blocks with dynamic sources , or custom-liquid sections or blocks
- using metafield definitions, or transfers, to create incoming dates
Either set a text dynamic source to the metafield definition holding the estimate restock date
Or add a custom-liquid block with {{ variant.next_incoming_date }} .
Otherwise with a vintage theme(non OS2.0) , you will need a theme customization to insert the line of liquid and style it, and update javascript when more than 1 variant.
An alternative is to show all variants next_incoming_date in a custom-liquid block to bypass needing javascript support:
{%- for variant in product.variants -%}
{%- if variant.incoming -%}
- {{ variant.sku }} arrives: {{ variant.next_incoming_date }}
{%- endif -%}
{%- endfor -%}
https://shopify.dev/api/liquid/objects/variant#variant-next_incoming_date
https://help.shopify.com/en/manual/products/inventory/transfers/receive-inventory