For origin in Area 1 (North and South America) there is a 7 day ticket issue deadline for D and A OneWorld Explorer fares. But for Areas 2 and 3 there is not pre-purchase requirement.

I have a DONE4 ticket issued on Friday night (8:30pm) and collected at the airport for departure on Sunday morning.

Ticket issue for these fares is pretty complex and tales quite some time and effort to get all the taxes correct. So I can understand why a TA prefers not to leave the issue process until the last minute. In my example above, the agent was expecting to issue an e-ticket, but ran into problems and eventually could only issue as a parper ticket for collection at the airport (for a A$50 fee).

But the OneWorld Explorer fare rules appear to show no pre-purchase requirements. Perhaps you could ask the agent to point you to the pre-purchase rule?

Note, however, that the business and first class OneWorld Circle Pacific fares does have a 7 date pre-purchase requirement no matter which continent it is purchased.