---
title: WakeAtTime
framework: driverkit
role: symbol
role_heading: Instance Method
path: driverkit/iotimerdispatchsource/wakeattime
---

# WakeAtTime

Schedules a callback from the timer.

## Declaration

```occ
virtual kern_return_t WakeAtTime(uint64_t options, uint64_t deadline, uint64_t leeway);
```

## Parameters

- `options`: The timebase to use when interpreting the deadline and leeway parameters. For a list of possible values, see doc://com.apple.driverkit/documentation/DriverKit/3242783-clock_types.
- `deadline`: The time at which to execute your action. The meaning of this parameter depends on the timebase you specified in the options parameter.
- `leeway`: The maximum amount of time beyond the scheduled deadline that the system may wait before executing your action. Leeway values improve the system’s power usage by letting the system schedule timers at a more advantageous time. The system guarantees the execution of the timer’s action before the combined deadline and leeway values expire.

## Return Value

Return Value kIOReturnSuccess on success, or another value if an error occurs. See Error Codes.

## Discussion

Discussion Use this method to schedule the execution time for your timer. Call this method from a block running on the same dispatch queue you passed to the Create method. If a previously scheduled timer has not yet fired, calling this method replaces the old time with the new value.

## See Also

### Rescheduling the Timer

- [Clock Types](driverkit/3242783-clock_types.md)