It is important to understand how Alerts operate. Alerts are handled by Telematics Guru, and not the device. They do not impact the device operation, or force uploads. (Devices can be configured to upload on certain conditions via OEM server however) 

For an alert email or SMS to be sent, the device data must be received by Telematics Guru, which then decides if an Alert State is "Active" or "Inactive" and acts accordingly. 

Users may experience delays in receiving the email or SMS on battery powered devices due to device setup. To best explain, we will work through an example:

Consider an Oyster 3G, which is set to Periodic Only uploads, only uploading 4 x per day, or every 6 hours. The user has set up a Geo-fence around their garage, as they want to be notified if their asset leaves this area. 

At 9am, the unit uploads according to it's heartbeat interval. 

At 9:30am, the unit starts moving and leaves the Geo-fence. There are no trip based uploads set up, so the next upload is...

At 3pm, the unit uploads according to the heartbeat - a Geo-fence alert will be sent now

This appears to be a delay in the alert of 5.5 hours. In order to avoid such behaviour, it is important to configure the device parameters so that changes in the values that affect your alerts will be uploaded in a timely manner. In this case we would want to configure the Oyster to upload on the beginning of it's trip.