Wiktionary
jam tomorrow
n. (context idiomatic English) Promised benefits that never arrive.
Wikipedia
Jam tomorrow
Jam tomorrow or jam to-morrow (older spelling) is an expression for a never-fulfilled promise. It originates from Lewis Carroll's 1871 book Through the Looking Glass and What Alice Found There. In the book the White Queen offers Alice " jam every other day" as an inducement to work for her:
Usage examples of "jam tomorrow".
You use big words to tell them its going to be jam tomorrow and they hope.