How soon does PEM hit after exertion?

[Rufous McKinney]

Cognitive exertion - especially talking/chatting with others...I get a rapid onset loss of energy and am almost in a coma, plus the strep level sore throat from using the voice.

But other PEM mostly seems to come on the next day. Lasts 48 hours typically...

using my eyes to see - like when I tried to paint...(for less than 30 minutes) I crashed the next day every time....

 

[Nord Wolf]

Physical or cognitive exertion instigates PEM the same day for me. If I overdo something a little, PEM sets in within 3 hours. If I overdo something a bit more than a little, PEM usually sets in within 1 hour. Though I have "rolling PEM", so it never really ends. The marker is if the ongoing symptoms suddenly increase.
However, if I have a night terror or ptsd episode while sleeping (which I always wake up from), PEM typically sets in immediately.

 

[Quest11]

For me it usually hits hard around 24 hours after with symptoms of pain, brain fog and fatigue but I will feel some degree of fatigue probably a few hours after.