It's possible to plant a dynamite near an objective but not close enough that it is registered by the objective. So no message and no problem so far. However planting another dynamite closer to the objective, close enough to be registered and messaged about after, can be triggered by the earlier dynamite. Allowing to blow up objectives with a message a few seconds before as opposed to 30 seconds.
Example. a barrier has a range of 5m. I plant the first dyna (A) at 8m. I wait 25 seconds to plant dyna B within the range. This results in a message about the dyna. Dyna A will trigger dyna B as it explodes, effectively giving the enemy team only 5 seconds.