I used https://make.powerapps.com to customize the "Lead to Opportunity Sales Process" business process flow.
I added the customizations to my Sales Customizations solution.
I wanted to add the (existing) Opportunity table to my Sales Customizations solution
I selected the Opportunity table and clicked the Next button
I clicked Add to add the table
I clicked the + New button to add a column to the existing Opportunity table
I added Trial Start (Optional)
I added Trial End (Optional)
I wanted to add an existing Business Process Flow to my Sales Customizations solution
I selected the "Lead to Opportunity Sales Process" business process flow and clicked the Add button
I clicked the Edit button up edit the Business Process Flow
I clicked the Add Stage button
I updated the Display Name to "Trial" and clicked the Apply button
I added a "Trial Start" Data Step
I selected the Required option
I clicked the Apply button
I added a "Trial End" Data Step
Again I selected the Required option and clicked the Apply button
I clicked the Update button
Validation was successful
I opened an existing Lead and Clicked the Next Stage button to move from Qualify to Develop
I created the (Lead) Opportunity
I clicked the Next Stage button to move the Business Process Flow from Develop to Trial
I clicked the Next Stage button again
I entered Opportunity|Trail Start and Opportunity|Trial End values and clicked the Next Stage button
The Business Process Flow moved to the Propose Stage
