Repeating 24 hour DeviceActivitySchedule behavior

My app uses a repeating 24 hour DeviceActivitySchedule defined like this:

let intervalStart = DateComponents(hour: 0, minute: 0, second: 0)
let intervalEnd = DateComponents(hour: 23, minute: 59, second: 59)
let schedule = DeviceActivitySchedule(
    intervalStart: intervalStart,
    intervalEnd: intervalEnd,
    repeats: true)

try center.startMonitoring(
      ACTIVITY_NAME,
      during: schedule,
      events: [...])

Both intervalDidStart and intervalDidEnd callback functions update CoreData and UserDefaults, and sometimes make network requests, and I'm worried that their close invocations may cause unexpected behavior.

Since intervalDidStart should be invoked only one second after intervalDidEnd, but intervalDidEnd may take longer than one second to run, due to updating local data and waiting for network requests to complete, how should this effect the invocation time of intervalDidStart? Is there a rule about the ordering of these functions, for instance if the interval is repeating and essentially overlaps like mine, is it guaranteed that intervalDidStart will always be called after intervalDidEnd returns, or is the behavior more undefined?