Separating egg yolks the night before beating meringue
Yes, that's fine - if you take a few precautions.

Once you have opened your eggs, you are exposing the contents to the air. So need to protect the eggs from drying out: A matching small jar or plastic container is a good choice for the yolks. For whites, you can even put them in your mixing bowl and cover tightly, which saves on cleanup.

You need not worry that your whites won't whip properly, many macaron bakers even recommend "aging" the whites, i.e. storing them for a day or so in the fridge. (But there is also a wild debate on whether this is really necessary.)

For food safety reasons, storing your separated eggs in the fridge is a must. And please remember that while you can certainly separate the eggs the night before, longer storage will affect the quality negatively, less so for the whites, but please use the yolks as soon as possible.