Every since we added Reminders support we have supported both Start and Due date within Informant. However Start date has always been problematic, especially with Exchange or Outlook users. There are two ways to deal with the timezones for start dates. When we handle it one way, we have one half of people for whom it breaks and the other half for whom it works great. If we handle it the other way, the opposite happens.

In 2015 we spent 2 days with Apple engineers talking to them about their support for the Start Date property of a Reminder. They recommended to remove the Start date from our interface because it was not tested and not guaranteed to work. 

As of Informant 4.9, we no longer support Start Date for Reminders because its not reliable - both in our own experience and straight from the Apple engineer's mouths.