Sforno on Exodus 16:21/ספורנו על שמות ט״ז:כ״א

1בבקר בבקר, each morning; the syntax is similar to that in Genesis 39,10 where the words כדברה אל יוסף יום יום mean: “when she spoke to him (thus) each and every day.” We also have a similar line in Exodus 30,7 when the Torah speaks about the daily procedure of cleaning the candelabra, writing בבקר בבקר בהיטיבו את הנרות, “every morning when he would clean out the lamps, etc.”

2וחם השמש ונמס, this was the reason that the people would gather it up early in the morning so that it did not yet have a chance to melt from the heat.