The Japanese description for Blue Mage's Nightbloom is:

自身の周囲の敵に無属性範囲魔法攻撃。威力 ：400
2体目以降の対象への威力は50％減少する。
追加効果 ： 対象に無属性の継続ダメージを付与する
威力 ： 75　効果時間： 60秒
リキャストタイマーを一部の青魔法と共有する。
The English description for Blue Mage's Nightbloom is:

Deals unaspected damage to all nearby enemies with a potency of 400 for the first enemy, and 50% less for all remaining enemies.
Additional Effect: Unaspected damage over time
Potency: 75
Duration: 60s
The English tooltip omits the last line of the Japanese tooltip and should include "Shares a recast timer with certain blue magic spells." Furthermore, Nightbloom does share a recast timer with another spell called Both Ends.