What will happen if a developer fails to mention the start date in the "From"...

If a developer fails to mention the start date in the "From" field when creating a price rule, the price rule will be saved. However, the price rule will not go into effect until the start date is added.

If a developer fails to mention the start date in the "From" field when creating a price rule in Adobe Commerce, the system will default to the current date, and the price rule will go into effect as soon as it is saved. The absence of a start date means there is no delay in the activation of the rule, and it becomes effective immediately upon saving.