   A  
 /   \
F     H
   A  
 /   \
F1    H1
|
H2
|
F2
+       IPreimageOracle oracle = VM.oracle();
+       if (nextPositionDepth == MAX_GAME_DEPTH - 1 && nextDuration.raw() > MAX_CLOCK_DURATION.raw() - oracle.challengePeriod() - CLOCK_EXTENSION.raw()) {
+           // Apply 1 CHALLENGE_PERIOD + 1 CLOCK_EXTENSION here. 
+           nextDuration = Duration.wrap(MAX_CLOCK_DURATION.raw() - oracle.challengePeriod() - CLOCK_EXTENSION.raw());
+       }
+       else if (nextDuration.raw() > MAX_CLOCK_DURATION.raw() - CLOCK_EXTENSION.raw()) {
-       if (nextDuration.raw() > MAX_CLOCK_DURATION.raw() - CLOCK_EXTENSION.raw()) {
            // If the potential grandchild is an execution trace bisection root, double the clock extension.
            uint64 extensionPeriod =
                nextPositionDepth == SPLIT_DEPTH - 1 ? CLOCK_EXTENSION.raw() * 2 : CLOCK_EXTENSION.raw();
            nextDuration = Duration.wrap(MAX_CLOCK_DURATION.raw() - extensionPeriod);
        }
