Jhoira, having the whole 'slow-time' aspect could have an activated ability like:
URXXX, tap jhoira; suspend target non-instant, non-sorcery spell for
x turns (target spell is exiled with
x time counters; at beginning of controller's upkeep, remove a time counter; when no time counters remain, spell resolves at the beginning of controller's next precombat main phase).
Maybe that is too powerful, and you should need to sac or
exile her instead of tap.
It would be new card mechanic design space though, eh?