Agreed - Reg. Z would permit you to go 180 days, 250 days or 777 days to first payment as long as f/c, APR, and payment schedule are disclosed accurately.
I think what they're referring to is Section 226.17(c)(4)(ii). This section says that in making disclosures and calculations, the creditor can ignore odd first payment periods that fall within certain parameters. For a loan between 1 and 10 years, you can ignore a difference in the first payment that is 11 days shorter or 21 days longer than the regular period. Thus, if a regular period is 30 days, you can ignore odd first payments of up to 51 days from the loan date.
In other words, Reg. Z permits you to pretend that the first payment period is the same as all the others if it's 51 days or less. That doesn't prohibit you from having a longer first payment period; it just means that if you have a longer first payment period, your disclosures have to take the extra time into account.
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