What was the common fund in the Jerusalem church and how long was it supposed to last?
The common fund was the shared common kitty of believing Jews in Jerusalem who sold their goods and lived together, expecting the King and Kingdom soon. It was a stopgap meant to last only until the King came and the Kingdom was set up; when Israel did not respond, the fund ran out.
Les explains that on the day of Pentecost and following, when Peter and the eleven preached, many Jews believed Jesus was the Messiah and that the Kingdom was coming. Because they expected the King to come as soon as Israel believed, they saw no reason to return to Babylon, Rome, Spain, or North Africa. So they stayed in Jerusalem and lived out of the common kitty. This was a stopgap measure until the King would come and the Kingdom would be set up. But Israel did not respond, the King did not come, and the kitty ran out. There was no runaway stock market or 25% interest, so the kitty went dry. The people ended up poor, having sold all their goods and being unable even to buy a ticket home. They were caught in Jerusalem, but God is just; they were in a legitimate cause because they had believed the Gospel of the Kingdom. God took care of them through the agreement Paul made with Peter, James, and John to remember the poor saints in Jerusalem wherever he went in his ministry.