Or HaChaim on Numbers 7:84/אור החיים על במדבר ז׳:פ״ד

1 ביום המשח אותו, on the day it was anointed. This verse is proof that our contention that all the princes had come to offer their gifts simultaneously on the first of Nissan is correct, but that G'd arranged that only one prince should offer his gift on any single day.

2מאת נשיאי ישראל, from the princes of Israel, etc. Why did the Torah have to write these words? Perhaps the Torah wanted to praise the princes for having acted spontaneously in order to inaugurate the altar. The word מאת is as if the Torah had written מאתם, i.e. that the idea originated with the princes and they had not been prompted. Our sages in Sifri volume 1 item 53 state that they all had an equal share in the single מצוה. What the sages meant was the offerings themselves were accounted as if they were a single offering. Different princes acquired different amounts of merit for their part in the offering, however. Nachshon's merit was the greatest of them all.