Antigonus Gonatas used mercs whenever possible. One of the reasons for the success of his reign was that he gave the Macedonians as much of a breather as possible to recover from Alexander and from the Diadochi wars. Macedon was as much fought over, literally, as anywhere in Asia. Perhaps more so.
To do this, he relied on mercs for garrisons etc. Gonatas also built a strong navy, that was able to wrest control of the Aegean sea from the Ptolemies. Instead of concentrating on building influence in Greece, the Ptolemies had to concentrate on their navy. And for Gonatas, this helped preserve his manpower.
This isn't to say that he didn't use the Macedonian levy. He did. But he tried to keep them out of things as much as possible.
Though I have little evidence for this, it does seem that the guard units are much reduced from the heyday of Philip and Alexander. The Hypaspists seem to disappear from the Antigonid military, and those elite units that can be identified, have far fewer numbers. Considering what we know about recruitment into these units, I would have to say that the recruiting pool had greatly shrunk. This would suggest that the standing Macedonian army as far as nationals went was much smaller.
Money could factor into this; the Antigonids were certainly the poorest of the three successor states.
And this could also mean that Gonatas found it preferable to keep the levy at home. This helped the economy, and made him popular by keeping them out of harms way.
I'm sure the levy would still be training for war. As evidenced by when they were called up. But Gonatas spared them whenever possible.