Spousal Cat B okay to be paid early to meet Financial requirement?

Hello Hello,
Quick question, my girlfriends visa runs out on the 23rd of January but we are just short of meeting the 18,600 earned over the previous 12 months. Her employer has offered to pay her early (on the 15th) for January. Can we use that pay-check to help us meet the requirement? Or is there some rule saying all the paychecks have to be perfectly spaced out by one month?
Thanks in advance!

bump

I think that would be okay, though her employer should explain the different pay date in their letter, so that UKVI aren't confused by why she hasn't been paid on the normal date.

After all, for Category B, you just need to show a total of £18,600 earned at any point in the last 12 months, from any and all jobs, so for that part of the requirement, it shouldn't matter WHEN she got paid.

For the other part of the requirement, since she hasn't been with her current employer for 6 months yet, she just needs to show that her current and future salary will be the equivalent of £18,600 per year, regardless of what date she is paid each month.