From a photographer's perspective, the most important thing for any photo shoot is light, so as long as you have got some of that - natural or constant studio lighting - you will be set to shoot anytime you feel like it.
Personally, my answer to that question would be slightly more complex as I primarily shoot with natural light. I simply believe that nothing highlights a woman's most attractive features as authentically as natural light. It gives such a beautifully natural glow to her skin and the lingerie that I prefer shooting when there is some daylight. Dependent on the shoot then, there are differences in the effects you will get to see in your images when using natural light:
Scheduling a photo shoot in the morning is ideal as there will definitely be sufficient light to create stunning images (even on a lousy, overcast British autumn day). Also, it helps you because you are not bloated from any food you ate throughout the day and you are fresh and awake. Morning sun makes for bright images and brings out colours very well.
Having an afternoon shoot is very similar to a morning one but the light generally makes for slightly softer and warmer images. It will give your skin a lovely natural glow as the afternoon light begins to fade. You could fit another gym session in to appear even more toned at your shoot but you would have to survive the day on light snacks to keep the balance between not bloating and not having a headache due to the lack of food.
Sunset / Evening Shoots
These are very special shoots, especially when you are lucky enough to have a beautiful orange and pink sunset which cloaks you in gorgeous light. You can create very edgy images playing with shadows or something extra special when incorporating some sparklers or fairy lights. Again though, you will have to watch your diet throughout the day and there is no guarantee for the sunset shots. This type of shoot is very dependent on the weather but twilight and lingerie make for an intriguing combination.
As you can tell, choosing the perfect time for your Boudoir shoot very much depends on the type of photographs your are after and the vision you have got in mind. A good photographer will talk to you about your ideas for your Boudoir images and the optimal shooting time to create the atmosphere you imagine.