How to suggest available appointment slots?

Hi,
We are trying to expose Simply Schedule Appointments functionality through Amazon Alexa skill. We are trying to cover functionalities like checking is the requested time available, suggesting some other slots and creating the actual appointment. Under the hood, we are using SSA plugin functions to have full compatibility, but there are few things that we are not sure if we are using it correctly.

1. Checking the time availability
Our users can ask for a particular time but we also want to give them several suggestions if the requested time is not available.

For this we are using \SSA_Availability_Functions->get_bookable_appointments($appointment_type, ['start_date_min' => $start_date, 'start_date_max' => $end_date]);.

What are the recommended values for ‘start_date_min’ and ‘start_date_max’? Should we load it from the appointment type data?

2. Time Zones
We do have our user’s time zone information. But it is not clear which one to use when calling SSA functions. Server, appointment type or is there some other logic to determine that.

3. Users
Do we need to import user information (create an account) into WordPress database or should it be able to accept ad hoc appointments?

Thanks