The curse of time directly skipped the Valkyries' timeline to the end of their lives.
This death looked scary, but out of the various victims cursed with the other six curses, this one had a fairly peaceful death.
After all, many Valkyries might not reach the end of their old life and die on the battlefield or something.
But these cursed ones finally reached the end of their lives... although it was manipulated, and they still died 'young' on the battlefield.
This wave of attack caught the Valkyries by surprise.
It wasn't as if they hadn't seen death like this or an attack like this, but the Valkyries guessed that Hydra should have sucked their life forces or something.
They didn't think that it was the curse of time, and Hydra also could only curse a lot less people with this curse compared to other curses.