Travel Boosts allow you to reduce the travel time of your sent Units by either 25% or 50%, depending on which Boost is selected. You can get Travel Boosts from the Black Market, within the "Items" section, under the “Boosts” tab.
Be aware: the effects of Travel Boosts CANNOT be combined or added together. Two Travel Boosts of 50% will not bring your Units to the target instantly. If applied consecutively, the first Travel Boost will cut the arrival time in half, and the second will then cut the remaining travel time in half again.