Q:
Superior Sigil of Concentration
It increases your boon duration by 33% chance for 7 seconds when you swap to a weapon with that sigil. This only affects new boons created after swapping weapons and while this boon’s effect is active.
[VZ] Valor Zeal – Stormbluff Isle – Looking for steady, casual-friendly NA raiders!
What Rising Dusk means is, when you swap to a weapon with this sigil, you gain a buff that last 7 seconds. Any boon you apply during this 7 second window lasts 33% longer. It is determined at the time of boon application, and does not dynamically update, so the boons keep the increased duration if applied during the 7 second window.