If a Green Lantern can create a power ring for someone else.
Can the Green Lantern then leave the new ring with that person indefinitely?
How long will the ring last?
Are there any example of this in any canon?
The duplicate is a real ring but the new recruit will have to share a Power Battery until they can get their own from Oa.
The new ring is not an energy construct. It takes material from the original ring and available matter to create a duplicate.
Green lantern rings (and the other rainbow corps) can Create both actual ring duplicates, with or without limitations built in, AND hard light constructs copies that will run out like any other lantern construct.