18 Then Moses entered the cloud as he went on up the mountain. And he stayed on the mountain forty days and forty nights.

Read Exodus 24:18 Using Other Translations

And Moses went into the midst of the cloud, and gat him up into the mount: and Moses was in the mount forty days and forty nights.
Moses entered the cloud and went up on the mountain. And Moses was on the mountain forty days and forty nights.
Then Moses disappeared into the cloud as he climbed higher up the mountain. He remained on the mountain forty days and forty nights.