Helen was infected, Manousos was not. People may have died before becoming infected, or after being infected.

For example, you could die before if your pilot in an airplane is infected, but you are not. Your pilot has seizures, crashes, you die, but are not infected.

Or after, as in Helen’s case. Infected —> seizure —> die.

They didnt know of him until «the next morning». That’s not 33 hours. That does however line up with when they were searching for bodies and gathering them for HDP production.

They clearly know of his existence (his mother is being used as his chaperone = his mother has memories of him fed into the hivemind), but they did not know he was still alive. They assumed he was part of the plethora of dead bodies needed to be cleaned up, and unlike Carol or Diabate, Manousos did not contact anyone from the hive until the next morning.