From Guild Wars 2 Wiki
“Double-click to gain a buff that increases your to chance gain  bonus experience from crafting by 50% for one hour.
— In-game description
- The boost increases bonus crafting experience, but does not affect experience towards leveling. In other words, you use fewer materials in order to gain crafting ranks.
- As with other consumables, the timer only counts down while the character is active; you do not lose any time while playing other characters or while logged out.