Is there any relation to what a denomination does with its time and the amount of time it spends in its General Assembly? Here are the lengths of of some recent GA's:
Associate Reformed Presbyterian Church (35,000 members): 3 day GA
Evangelical Presbyterian Church (75,000 members): 4 day GA
Presbyterian Church in America (338,000 members): 4 day GA
Orthodox Presbyterian Church (28,000 members): 8 day GA
Just by way of comparison, the EPC's 4 day GA agenda is posted online here while the OPC's 8 day GA report is here.