1)
When did Hashem spread a cloud?
1.
Radak: It is when Yisrael left Egypt. Hashem traveled in front of them "Yomam b'Amud Anan" (Shemos 13:21).
2)
What is "l'Masach"?
1.
Radak: It is not a cover above, rather, like a curtain in front of them. The same applies to "v'Es Masach ha'Pesach" (Shemos 35:15). The cloud was in front of them when they traveled, but when they rested, it was over them, until they traveled again. Or, perhaps "l'Masach" includes when traveling and when resting (it was in front of them).
2.
Malbim: In addition to the cloud and fire in front of them, like the Torah says, clouds were over their heads and around them, like Chazal said.
