Formula for showing difference between the earliest custom date entered in a task for a project and the oldest custom date entered

When we have a new market to add or have to remove an existing market, we create a new project for that market.  Within that project, we will have multiple custom tasks for different aspects of the market, and as part of that task is a custom date field for "Speed to Market"

So for example:

Project A:

Task 1 - Speed to Market = 10/22/2025

Task 2 - Speed to Market = 10/1/2025

Task 3 - Speed to Market = 10/15/2025

I am trying to create a formula that will take the earliest speed to market (by project) and get the date difference with the latest speed to market. So in this case, for project A the difference would be 10/22 - 10/1 = 21 days.  

Any help on figuring out this formula would be great. I know there is already an issue with excluding weekends/holidays but want to start trying to work on this portion before resorting to external reporting methods.