It seems that all four of the following forms are used:
flextime
flex-time
flexitime
flexi-timeThe preferred term varies from country to country. According to the Corpus of Global Web-based English,
flex-time is used most in the US and Canada, followed closely by
flextime. Britain, Ireland and New Zealand favour
flexitime, with
flexi-time second favourite. Australia appears to use
flexi-time most often, and then
flextime and
flexitime. However the numbers are fairly small, so the ranking is not necessarily totally reliable.
Given the geographical variation, I don't think either of the versions allowed in Chi (that is, the un-hyphenated ones) could be said to be a common word, especially considering that none of these words are used all that often anyway, as TRex points out. So I'm going to make
flexitime and
flextime rare, and remove
flexitime as a nine-letter seed word.
The fact that
flexitime was played by a lot more people than
flextime, as MK tells us, would partly be explained by the fact that most players put a lot of effort into getting the niner, and tend to keep struggling with a puzzle until they do. (And, dare I say it, resorting to an anagram site is all too easy when all else fails.) Also there are a lot more players from Australia than anywhere else, and I think
flexitime is more familiar here, as Les says.
In conclusion, I'd like to quote one of the few US examples that uses the
flexitime version, from the Washington Monthly in 1995:
A 1981 Monthly article detailed a similar trip to the Labor Department to investigate a program called "flexitime," which gave workers greater flexibility in their hours and working conditions. Flexibility proved to be an understatement: Ringing phones were going unanswered as radios blared. Secretaries were reading novels and knitting. A woman padded toward her office in fuzzy bedroom slippers. Nine phone calls to department employees found all of them "out of the office."
If that's what things were like in the Labor Department, imagine what it must have been like in the Relaxation Department.