Wanted to amend, I also do this with my spouse. One single off-cycle paycheck at the end of year, as a spouse can also be included in your Solo 401k. Then the spouse has their contribution maxed out plus employer contribution (subject to % rules).

I used to contribute each paycheck but it's easier to do this at the end of the year, as you can decide exactly how much you're able to contribute based on how your business has performed.