Since you are not going to be harvesting any honey from a hive of packaged
bees any time soon, it would be best to treat immediately, preventing any
problems.  If the hive starts looking like it might produce a surplus,
remove any medication before putting on honey supers.  As a rule you can
expect a new hive from package bees starting out on foundation to do well
if they draw all comb in two hive bodies and fill the upper with honey for
winter stores.  This is especially true with the great demand for packages
and the late spring deliveries we're experiencing this year.
 
Ted Wout, 3rd year, 10 hives
Red Oak, TX