www.ismaili.net

Also, on Friday many special events had happened, this is the reason Friday is significant for Muslims. And for (What I think, reason for fasting) Ismailis if Chandraat comes on Friday than its like double happiness, and people tend to enjoy and will eat lots of food which might not good for health....

Might be this topic explained in Imam's farman other than (other) religious books. These links might help you for other information, but you might have to search for detail. https://www.google.ca/search?q=Chandraat+philosophy+ismaili&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:offic...