If >= 0, this value will override the CheckpointSaveMaxMSPerFrame member variable, which is the maximum time allowed each frame to spend on saving a checkpoint. If 0, it will save the checkpoint in a single frame, regardless of how long it takes.
Usage
demo.CheckpointSaveMaxMSPerFrameOverride [value]
Set via the console (~) or in DefaultEngine.ini / DefaultGame.ini.