Even if you can’t be a shliach for 24 hours a day, be a shliach for some amount of time. But you must be a real shliach during that time.
Everyone must take upon himself to do mivtzoim, to work on various things like spreading chassidus or spreading yiddishkeit… No matter what your job is, you must know that you’re a soldier, there’s no ‘I have no energy today’.
It’s not our business to think about the things that Hashem does, and to offer explanations for them; our job is to know one thing, “yotzei l’milchemes beis dovid”, to enter the Rebbe’s army, and that’s all.
Questions often come from a lack of knowledge. If we’d learn the maamorim with the sichos we have from the Rebbe, and especially if we’d learn the igros kodesh which the Rebbe wrote, then we can see the Rebbe’s approach to various things from those letters.
It’s not really a matter of quantity, it could even be ten minutes, but those ten minutes must be done right. Learn something of the Rebbe’s Torah every day.