There's no single best way to craft an after hours greeting. The most important point is that you equip your customers with what they need to know, and give them an avenue to contact you, whether that's through voicemail, email, or other channels.
In a concise fashion, you should relate the hours your business functions, and note any potential conflicts such as holidays or business closures. Use an auto attendant if you have more than one menu option for the customer, such as a voicemail box and an emergency support line.

Here’s a simple fact. If you don’t leave a voicemail, you aren’t going to get a call back. Still, a lot of salespeople don’t leave voicemails, assuming their call won’t get returned, or the prospect won’t listen anyway. But what if they’re wrong? What if the prospect does listen and does call back? Or, what if after a few voicemails they decide you might be the service provider they need? We can assure you that if you aren’t leaving a message, then your prospect won’t know who you are, why you called, or what you have to offer them. And we could be wrong, but if you plan to make a sale, you probably need to talk to your customer.
The bottom line is that a business’s situation is likely to change often and rapidly, each of which need a unique and applicable voicemail greeting to cover the circumstances and timeline. For example, callers shouldn’t reach a business-as-usual voicemail, and therefore expect a return call within the business day, if the subject they’re calling is out on vacation for two weeks. Such a lack of communication is a recipe to lose that caller’s trust and tarnish the brand’s reputation.