hoursBetween() returns zero

hoursBetween() returns zero

Why does this code:
  1. info current_date_time_zoho;
  2. info customer_sent_email_on;
  3. info hoursBetween(customer_sent_email_on, current_date_time_zoho);

Produce this result with hours being zero? The answer should be 3.

  1. 2023-09-11T17:16:19-05:00
  2. 2023-09-11T14:58:51-05:00
  3. 0