Or HaChaim on Exodus 14:21/אור החיים על שמות י״ד:כ״א

1 ויט משה את ידו, Moses inclined his hand, etc. Although the Torah reports that G'd made a strong east wind blow all night which dried out the sea, this referred only to the deep waters. G'd did not want the Israelites to have to descend to the very depths and to have to get tired by walking too far. This is why He first "froze" the deep parts of the sea by means of the east wind. If not for this consideration, G'd would have dispensed with the east wind altogether.

2It is of interest to know whether Moses inclined his hand as a signal for the sea to split at the beginning of the night or at the end of the night. From the wording of the verse we may almost prove that it was close to morning. This is difficult, however, because if it was so how could one discern that the splitting of the sea was brought about by Moses' action? We therefore have to understand the verse thus: "Moses inclined his hand after G'd had already made an east wind blow during the whole night which dried out the (deeper) parts of the sea;" as soon as Moses inclined his hand the waters split. This would then be in line with my commentary on verse 15 that all this occurred after Nachshon had waded into the sea in response to G'd's challenge to demonstrate an act of faith. Moses had held off with inclining his hand until after Nachshon was in the sea. The Israelites then followed when the sea split. This also conforms to the way Shemot Rabbah 21 describes what happened. Another way of explaining the sequence of events is this: when the Torah writes "He turned the sea into dry land," all the waters of the sea crystallised in such a way that the Israelites did not need to descend into the bed of the sea, whereas the east wind had dried out all the waters of the sea. I consider the first explanation as more likely to be correct.

3כל הלילה, all night long. The wind blew all night and the sea split at the end of the night causing the Israelites to begin marching through it.