Inaccurate 'Interruption will be sent' messaging

**Issue**
* Events channel says Interruption will be sent in 15 seconds, but the time is usually longer by more than 5 secs (>33% of estimate).

* From ReadMe:
```
2022-05-18T11:39:45: ✅ Rebalance Recommendation sent
2022-05-18T11:39:45: ⏳ Interruption will be sent in 15 seconds
2022-05-18T11:40:05: ✅ Spot 2-minute Interruption Notification sent
2022-05-18T11:42:05: ✅ Spot Instance Shutdown sent
```

**Expected Outcome**
* Timestamp diff between 'will be sent' and 'sent' should be closer to 15 seconds
OR
* Log sent to events channel updated, ex: "⏳ Interruption will be sent in 15-X seconds"