Our vacation policy for years was this: Take some!
But then we noticed that some employees weren't taking enough vacation and just powering through and getting burned out, so now our policy is this:
10 paid switched-off days a year. 5 paid working-vacation days a year. 10 paid national holidays a year. 5 weeks total.
Of course we follow regional labor laws, so our full policy has a lot more legalese in it, but that's not the point, the point is to capture the spirit of each policy.
In general, I don't care when you work or even how much you work. What I care about is that you do your best work, at a good pace, sustainably. We care about results, not hours-spent working. Some people call this ROWE.
Sustainability is why we created the policy, to make sure everyone DOES take time to relax every few months, to disconnect and recharge.
Since we don't have deadlines, I encourage people to set their own schedule, spending time with family, pursuing hobbies, or just plain relaxing when it's most convenient to them.
Bottom line: It's never a good time to take vacation, so take it when it's most convenient for you.
It would be great if you made sure support was covered while you're out, but worse comes to worse, that's something that I (as the CEO) can cover, I'm rarely totally on vacation. I'm also not worried about people taking too much time away from work all at once, as being gone for 4 weeks straight impacts their pace quite a bit. But people are encouraged to go work from a vacation spot and only work half-days for a while, that's what I do every summer!