Sorry, @mjp44 – Zoom now limits all meetings on Basic/Free accounts to 40 minutes, including 1:1 meetings. See this announcement from Zoom regarding recent changes:
https://support.zoom.us/hc/en-us/articles/5809097508109
If your unlicensed account is attached to an account with some paid users, you might be exempt from this new limit.
Please ask your student to exit the meeting from one device and wait 15-30 seconds before rejoining with the second device. Otherwise, Zoom servers will interpret his second login as a third person on the call since his first connection has not fully been closed out. It takes Zoom some time to recognize this – today under a minute after the first connection is terminated. As you have noticed, having a third person in the meeting at any time will trigger the 40 minute time limit under any circumstances for a basic/unlicensed account.