Charles Ellicott Commentary Exodus 24:16

"And the glory of Jehovah abode upon mount Sinai, and the cloud covered it six days: and the seventh day he called unto Moses out of the midst of the cloud." — Exodus 24:16 (ASV)

The seventh day he called to Moses from within the cloud. —Moses, it is evident, would not enter the cloud without a positive summons. It pleased God to put off the summons for six days. Moses doubtless employed the time in such prayer and meditation as rendered him fit for near contact with Deity.