You could raise 2 people quickly. Or I'd pop it before reraise so I'm not caught casting it when someone needs a cure. I usually try to reapply during downtime when it's still up, but occasionally get caught without it.

I'd prefer a job trait that allows simultaneous casting of at least two spells at once at all times, with normal casting time (modified by FC of course). I know that's the traditional suggestion for Doublecast and it's often criticized as impossible to implement, but I never buy that. It would cut down on time spent buffing, if you're cycling refresh and haste anyway. It would also give RDM the unique ability to not worry about what else might happen after they start casting something long like raise/reraise.

The big issue would be equip swaps. If I see the need to emergency cure while casting a tier IV nuke, I'd still be tempted to wait until the nuke was finished so I don't get it off with Surya's on. This would be a potential problem with lots of spell combos.