reduce default value for keep_checkpoint_every_n_hours to 0.5 from 0.1, which produces too many checkpoints by default
reduce default value for keep_checkpoint_every_n_hours to 0.5 from 0.1, which produces too many checkpoints by default

PiperOrigin-RevId: 186701847

google/deepvariant,google/deepvariant,google/deepvariant