I think we not need additional field.
We have currently Creature::m_needNotify that set to true if grids updates detect for example player move in visibility range
This flag let call Creature reaction not from deep call stack place but from main server loop, from Creature::Update
Sometime ago has been discussed replacing this bool variable by time_t variable
this let for example proccess reactions not at next tick but for example one in 2-3-... ticks for CPU less load, without visible changes for players
In this case field set to now + reaction_delay (possible from config) if not set to time > now currently,
and Creature::Update call reaction proccessing only when time expired.
It easy can be reuse also for aggro delay at respawn: just at respawn set timer = now + 5 secs