Google Calendar + Slack Integration

Zapier's Google Calendar trigger fires when an event starts, not before. To get a 15-minute advance reminder, you need to add a Delay step that calculates the time difference and waits.

This is imprecise — the delay drifts by several minutes depending on Zapier's processing queue. Make's scheduled approach is actually better here: it polls for events starting in the next 15 minutes, which gives you precise advance notifications.

You set a scenario to run every 5 minutes, checking for events that start within the next 15-20 minutes. When it finds matching events, it sends the Slack message immediately.

The polling interval is your precision — poll every 5 minutes and your reminders are accurate to within 5 minutes. This is good enough for meeting reminders.

When you poll for upcoming events every 5 minutes, the same meeting will appear in multiple polling intervals. Without deduplication, you will send 3-4 reminders for the same meeting.

Make handles this with its built-in Data Store — mark events as "notified" so they are not processed again. Zapier avoids this problem because its trigger only fires once per event, but sacrifices timing precision.

n8n requires you to implement deduplication manually using a database or static data node.

Google Calendar API allows 1,000,000 queries per day. Even polling every minute across 10 calendars, you will use about 14,400 queries per day — well within limits.

There is no practical API rate limit concern for calendar automations.

A team of 20 people with an average of 5 meetings per day generates 100 reminder operations per day, or about 2,000 per month. Make's free tier covers this.

Zapier would need a paid plan. n8n self-hosted handles it at zero marginal cost.