In social work, doorknobbing is the word sometimes used to describe the phenomenon of delaying the important personal revelations until the end of the therapy session when goodbyes are being said.
This option has the advantage of actually being in circulation. It has the disadvantage that it also carries one or two very different meanings of a frank sexual nature.
1. Did "long time no see"
arrive in U.S. English from forms of pidgin English
spoken separately by both some Native Americans
and some Chinese immigrants?
The earliest recorded examples are from native Americans, but it's plausible it was used in other types of pidgin English at the same time.
2. When did this
turn of phrase first gain the recorded notice of an
American English-speaking author?
It has been recorded by American English-speaking writers in 1900. The author Raymond Chandler used it in a 1939 newspaper and 1940 book.
3. When did the phrase cross over into use by native U.S.
English speakers among themselves?
Chandler presumably helped popularise it with detective stories and film noir of the early forties.
The OED says it's a "Colloq. phr. (orig. U.S.) long time no see, a joc. imitation of broken English, used as a greeting
after prolonged separation."
Their earliest quotation is 1900 from a native American:
1900 W. F. Drannan Thirty-one Years on Plains
(1901) xxxvii. 515 When we rode up to him [sc.
an American Indian] he said: ‘Good mornin. Long
time no see you.’
Their next quotation of 1939 shows it was fully naturalised:
1939 R. Chandler in Sat. Evening Post 14 Oct. 72/4
Hi, Tony. Long time no see.
Their next is also from Chandler, in 1940's Farewell, my Lovely.
Best Answer
It's idiomatic, but it's not an idiom—a phrase or usage whose meaning is not determined by the meanings of its parts. You can use less than readily with just about any adjective which denotes a measurable quality:
As the Comments suggest, less than eager is ordinarily used in an ironically understated sense more or less equivalent to strongly averse.