If you have a brd/mch in the party, it shouldn't be an issue. If you have to use it off cd, just use it in the least invasive way possible to not ruin your own dps. Typically after your b4, before the t3 refresh. This is an ogcd clip, and is a dps loss over time, but the only way to manashift without loss is to have a thundercloud proc available while in Umbral ice to weave the mana shift.