From GridLAB-D Wiki
TECHNICAL MANUAL
The checkpoint_interval global variables specify how often checkpoint images are saved. The checkpoint interval can either be based on the wall clock or the simulation clock depending on the setting of checkpoint_type global variable.
GLM
#set checkpoint_interval="3600"
Command line
host% gridlabd -D checkpoint_interval=3600
Version
Checkpoints were introduced in Version 3.0.