why wasn't the articles of confederation adopted for 5 years?

Trying to come together as a unified nation was very difficult. Before the Articles of Confederation, each of the 13 colonies was in many ways autonomous entities. Each of the delegates had his own ideas about the proposed new nation. Therefore, it took 5 years to hammer out their differences and come to a compromise.

Also, remember that traveling to the convention was a long and arduous journey for most of the delegates.