Using the same variable between if-statements within loop()
Make the variable global, thus put it outside the loop function; also you don't need the static keyword anymore.

float RewardTime = 0;


Than inside your first if statement, remove the static float keywords:

RewardTime = (Serial.parseFloat() * Scale) + Base;


Some other tips:


normally local variables do not start with a capital (so rewardTime is like most coding conventions)
Always use brackets.

if (State == LOW)
  State = HIGH;
else
  State = LOW;


Change to:

  if (State == LOW)
  {
    State = HIGH;
  }
  else
  {
    State = LOW;
  }



However, to make it more simpler, use the ternary operator, you can change it to:

State = (State == LOW ? HIGH : LOW);


Which means: if some condition ? Do this : Else do this;