Witchipedia

Absolutely not. There are some very good reasons to do magick at night, but they don't apply to everyone.

Traditionally covens met under the cover of darkness to do magick in order to avoid detection - to keep their work a secret. It was a matter of convenience in a time when there wasn't a lot of outdoor lighting and the neighbors were likely asleep. If your privacy can be better assured during the day when the neighbors are at work, then day time is best for you.

One other consideration to take into account is the fact that people are more open to suggestion when in an altered state of consciousness. More simply put - it's easier to cast a spell on someone else while they are sleeping. If your spellwork isn't aimed at someone else, this isn't something you need to worry about at all.

Personally, I find dawn to be the best time for work. There is no doubt about what planetary hour I'm in, the kids aren't up yet, the air is alive and wonderful and all the neighbors are too busy doing trying to get to work on time to wonder what I'm doing in the back yard. If I am out there at night, they're peering over the fence with a flashlight in one hand and a shotgun in another to make sure I'm not a coyote (and to their credit, it would be my livestock they'd be protecting, bless them) or a thief/rapist/cow tipper etc.