Subscribed calendars do not get pushed. The subscriber's calendar app pulls. The interval between pulls is set by the app, not the publisher.
Here is what each major app actually does.
Apple Calendar (iOS, iPadOS, macOS)
Apple Calendar checks subscribed feeds about once an hour by default. The user can change it to 5 minutes, 15 minutes, hourly, daily, weekly, or never. Most users leave it on hourly.
This is the fastest of the major calendar apps. For a typical weekly schedule, Apple subscribers see every edit within 60 minutes.
There is no setting for the publisher to make the refresh faster. The cadence is per-subscriber, per-device.
Google Calendar
Google Calendar checks subscribed feeds every 12 to 24 hours. There is no user setting to make it faster. There is no publisher setting either.
This is the cadence that surprises new publishers. An event added on Monday afternoon may not appear in Google subscribers' calendars until Tuesday morning. For most schedules this is fine because the next event is still days away. For last-minute changes it is not fine.
Google does this to limit how often its servers reach out to third-party feeds. There is no way around it.
Outlook and Microsoft 365
Outlook on the web and Microsoft 365 sit in the middle. Refresh happens every 1 to 4 hours, depending on the account type and load.
Outlook desktop is similar but can be slower if the app is closed.
What this means for publishers
Plan around the slowest subscriber, which is the Google one.
For a normal weekly schedule, the polling cadence is invisible. You add events days or weeks in advance. Everyone sees them well before they happen.
For edits inside the next 24 hours, the cadence matters. A practice cancellation announced 30 minutes before start time will reach Apple subscribers in time but will not reach Google subscribers in time. For those cases, send a one-off email or text too.
Calfeed will eventually add an out-of-band notification path so a single edit can fire both the feed update and an email blast to subscribers who opted in. Until then, treat the calendar as the source of truth and the text message as the emergency channel.
What subscribers can do
Subscribers on Google cannot speed up their own polling. The setting does not exist.
Subscribers on Apple can drop their refresh interval to 5 or 15 minutes for a specific calendar. Right-click the calendar in the sidebar, pick "Get Info", change "Auto-refresh".
For most groups, hourly is fine. For one urgent calendar, ask Apple subscribers to set it to 15 minutes.
Test a subscription link before you share it.