Modern world is a global world. If a foreigner needs to offer you a deal and ensure that you can listen to him in a right time and in a right mind, he must contact you at time when there is daytime in your country. Same thing goes for you if you want to finalize a deal with a foreigner.
In business, time is not seen when it comes to work. The only thing that is seen is requirement. It is important to be aware of every timezone that suits your requirement.