They will count back 12 months from the DATE OF APPLICATION to determine if he met the financial requirement in the US. So if they apply April 1, he needs to have made a minimum of £18,600 between April 2, 2016 and April 1, 2017 (in his case December 17, 2016). Sounds like he will easily meet that requirement.
It's fine for his UK job to be a fixed contract, just so long as it is continuing for the foreseeable future (which is certainly the case for a 1-2 year contract). Just be sure he does NOT leave that job until his spouse has landed in the UK. Easier to "not go there." As soon as she's landed, he can feel free to quit and find something that's a better fit.
