Siri: How to add an item to specific Reminders list AND set a reminder time?
Check this question for the sentence structure you need to use to achieve this:
How to add a reminder to a specific list and time via Siri

Add &quot;list name&quot; reminder &quot;new item&quot; on &quot;date and time&quot;
Example: &quot;Add activities reminder basketball practice on friday at 2pm.&quot;