Karlie here from the Shopify Guru Team! What you can do is add in the shipping time as your shipping rate Name. If you were to add a shipping rate, or edit an already existing rate you would do so from your Shopify Admin> Settings> Shipping. You can see more about how to add shipping rates, here! As an example, you could name a shipping rate "2-3 Days Standard Shipping" or something along those lines.
I hope this helps, but if you have any further questions - be sure to ask and we would be happy to help!
Would like to know couple of things.
If we put ourselves in place of a customer, what we consider is "when I will get this product?" For this, how can we put very close shipping time? It will not be a good idea when we say 7-10 days and it takes twice of that. How do we do it correctly? Also, what about tracking number. if any? Thanks.