It sounds like, at this time, neither of them are fixed, in which case you should not let them out together to avoid unexpected pregnancies. It does not take long and rabbits are very wired to mate and protect, so you want to make sure they are separated while both are not fixed.
There is a hormonal spike following a neuter, and typically it’s recommended to wait a month to allow it to normalize, so if he’s getting neutered in December, and then she will be spayed in January (and then she’ll need a couple weeks to recover), I would just wait until both are fixed and recovered to start interactions. Until then, you can do a lot of prebonding, like cage swapping and item swapping.
The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.