Workflow Trigger Based on Meeting Time

It would be nice to be able to set workflow triggers based on the exact time a meeting is scheduled.

For example, we would like to be able to trigger an SMS reminder that the meeting John Doe scheduled with us starts in 15 minutes. As of now, we can only trigger actions a day before the date of the meeting at a specific time. We cannot trigger actions based on the exact time of the meeting itself, nor anything within the day of the meeting.