短暂和稍纵即逝的意思都是形容时间很短,但是相对来说,稍纵即逝的时间要更加短暂些:Brief and fleeting time, both of described time is short, but relatively speaking, the fleeting time is short more and more.For example,(短暂)youth is short,time is short,i need to go;(稍纵即逝)rainbow is always fleeting.
on the whole,you just remember that the time of fleeting is less than short is ok.