Customizing a schedule's execution timezone

Schedules that don't have a set timezone will, by default, execute in UTC. By the end of this guide, you'll know how to:

• Set custom timezones on schedule definitions
• Set custom timezones on partitioned jobs
• Account for the impact of Daylight Savings Time on schedule execution times

note

This guide assumes familiarity with:

• Schedules
• Jobs, either asset or op-based
• Partitions

Setting timezones on schedule definitions

Using the execution_timezone parameter allows you to specify a timezone for the schedule on the following objects:

• @dg.schedule
• ScheduleDefinition
• build_schedule_from_dbt_selection

This parameter accepts any tz timezone. For example, the following schedule will execute every day at 9:00 AM in US Pacific time (America/Los_Angeles):

my_timezone_schedule = ScheduleDefinition(
    job=my_job, cron_schedule="0 9 * * *", execution_timezone="America/Los_Angeles"
)

Setting timezones on partitioned jobs

Schedules constructed from partitioned jobs execute in the timezone defined on the partition's config. Partitions definitions have a timezone parameter, which accepts any tz timezone.

For example, the following partition uses the US Pacific (America/Los_Angeles) timezone:

from dagster import DailyPartitionsDefinition

daily_partition = DailyPartitionsDefinition(
    start_date="2024-05-20", timezone="America/Los_Angeles"
)

Execution times and Daylight Savings Time

When Daylight Savings Time (DST) begins and ends, there may be some impact on your schedules' execution times.

Impact on daily schedules

Because of DST transitions, it's possible to specify an execution time that doesn't exist for every scheduled interval.

Let's say you have a schedule that executes every day at 2:30 AM. On the day DST begins, time jumps from 2:00AM to 3:00AM, which means the time of 2:30 AM won't exist.

Dagster would instead run the schedule at the next time that exists, which would be 3:00 AM:

# DST begins: time jumps forward an hour at 2:00 AM

- 12:30 AM
- 1:00 AM
- 1:30 AM
- 3:00 AM ## time transition; schedule executes
- 3:30 AM
- 4:00 AM

It's also possible to specify an execution time that exists twice on one day every year.

Let's say you have a schedule that executes every day at 1:30 AM. On the day DST ends, the hour from 1:00 AM to 2:00 AM repeats, which means the time of 1:30 AM will exist twice. This means there are two possible times the schedule could run.

In this case, Dagster would execute the schedule at the second iteration of 1:30 AM:

# DST ends: time jumps backward an hour at 2:00 AM

- 12:30 AM
- 1:00 AM
- 1:30 AM
- 1:00 AM ## time transition
- 1:30 AM ## schedule executes
- 2:00 AM

Impact on hourly schedules

Hourly schedules are unaffected by daylight savings time transitions. Schedules will continue to run exactly once an hour, even as DST ends and the hour from 1:00 AM to 2:00 AM repeats.

Let's say you have a schedule that executes hourly at 30 minutes past the hour. On the day DST ends, the schedule would run at 12:30 AM and both instances of 1:30 AM before proceeding normally at 2:30 AM:

# DST ends: time jumps backward an hour at 2:00 AM

- 12:30 AM ## schedule executes
- 1:00 AM
- 1:30 AM ## schedule executes
- 1:00 AM ## time transition
- 1:30 AM ## schedule executes
- 2:00 AM
- 2:30 AM ## schedule executes

APIs in this guide

Name	Description
@dg.schedule	Decorator that defines a schedule that executes according to a given cron schedule.
ScheduleDefinition	Class for schedules.
build_schedule_from_partitioned_job	A function that constructs a schedule whose interval matches the partitioning of a partitioned job.
build_schedule_from_dbt_selection	A function that constructs a schedule that materializes a set of specified dbt resources.