Most speed boost items (including building speed, shipbuilding speed, repair speed, research speed and scan speed) will not affect processes already underway. They only affect newly started projects.
Boosts increase the speed of a particular operation by a certain ratio, rather than reducing the completion time. Sometimes this can make the time reduced look incorrect if you're not familar with how it works. Example: With a shipbuilding speed boost of 25%, plus a shipbuilding research technology speed boost of 10%, the speed of building ships will be increased +35% = 1.35x, which works out to reducing the total shipbuilding time to 74% of the original time. [1/1.35 = 74% of original time]