Dispatch Source timer schedule timout - swift

Question

With the following Swift code, I'm trying to create a task that runs every hour:
let queue: DispatchQueue = .main
let timer = DispatchSource.makeTimerSource(queue: queue)
timer.schedule(deadline: .now(), repeating: .seconds(3600), leeway: .milliseconds(100)
timer.setEventHandler { [weak self] in
// run code
}
Now, when I have the repeating set at a lower number, say 10 or event 150 seconds, it triggers as expected both in the foreground and background (or, rather, once the foreground hits it triggers, if the timer went off while in the background).
However, when I let the app timeout to the lock screen, and wait for an hour, it doesn't display.
Is there some timeout that Apple has for DispatchSource schedules? If so, what is it? And is there any way to change or get around it?
Edit
I don't want special functionality when it backgrounds, I want the code to keep running as normal and to trigger the event handler when the timeout happens, even if it's in the background

Answer 1

I ended up taking matt's suggestion and saving the time every time the code gets called, as seen below. Worked well!
let timeOfLastCheck = Date()
let queue: DispatchQueue = .main
let timer = DispatchSource.makeTimerSource(queue: queue)
timer.schedule(deadline: .now(), repeating: .seconds(3600), leeway: .milliseconds(100)
timer.setEventHandler { [weak self] in
timeOfLastCheck = Date()
// run code
}
And elsewhere, where the timer is actually getting created:
let notificationCenter: NotificationCenter = .default
let activeNotificationToken = notificationCenter.addObserver(
forName: UIApplication.didBecomeActiveNotification,
object: nil,
queue: nil
) { [weak self] _ in
let now = Date()
if let `self` = self,
let timeInterval = TimeInterval(dispatchTimeInterval: self.interval), // TimeInterval is extended elsewhere to be able to take in a DispatchTimeInterval in the init
now > timeOfLastCheck.addingTimeInterval(timeInterval) {
self.timeOfLastCheck = Date()
// run code
}
}