Chasidut к Бамидбар 3:30

In his comment on the words ‎ודתן ואבירם‎, Rashi adds ‎that whereas these members of the tribe of Reuven had been ‎angry that their tribe had not been accorded the privileges due to ‎the first born, i.e. their founding father Reuven, Korach was ‎angry at not having been appointed as the leader of Kehatites, ‎rather than Elitzafan ben Uzziel whom Moses had appointed at ‎G’d’s instruction. (Compare Numbers 3,30). Rashi explains ‎that Korach felt slighted, feeling that since he was the first born ‎son of Yitzhar who was the second son of Amram, this position ‎was rightfully his, seeing that Elitzafan son of Uzziel was the son ‎of someone junior to his father.‎
Our author wonders that if Korach’s dissatisfaction had dated ‎back to these appointments described by the Torah in the third ‎chapter of Parshat Bamidbar, why had he not complained at ‎that time?
Our author answers this by reminding us that at ‎that time, before the episode with the spies, when it was assumed ‎by the people that they would all enter the Holy Land and secure ‎their ancestral heritage there, the position of tribal head or even ‎that of head of one of the three sections of the Levites, would ‎prove to have been a very temporary position, as entry into the ‎land of Israel was expected to take place within less than a year. ‎Now that they were condemned to spend 40 years wandering in ‎the desert this position carried with it far more importance. ‎Korach’s jealousy therefore had been aroused at this time.‎