List of differences:
- defer means to do at that time, incubate reminds you merely. maybe you will do it, maybe you will re-organize, who knows? we will see. just remind me at that time.
- incubate in the tickler means: invisible. it is a difference if I see an upcoming event daily, because it is in the calendar and I can see each morning that it is coming in 8,7,..5...2.. days.. today! In the tickler it suddenly just pops out: oh yeah.
- defer can also be day-specific. The point is: you said you will do it at that time, against just being reminded.